How to make the previous day from today to be readonly?

Here is the calendar javascript code

monthMaxDays	= [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
            monthMaxDaysLeap= [31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
            hideSelectTags = [];

function getRealYear(dateObj)
            {
                return (dateObj.getYear() % 100) + (((dateObj.getYear() % 100) < 39) ? 2000 : 1900);
            }

function getDaysPerMonth(month, year)
            {
                /* 
          Check for leap year. These are some conditions to check year is leap year or not...
          1.Years evenly divisible by four are normally leap years, except for... 
          2.Years also evenly divisible by 100 are not leap years, except for... 
          3.Years also evenly divisible by 400 are leap years. 
                 */
                if ((year % 4) == 0)
                {
                    if ((year % 100) == 0 && (year % 400) != 0)
                        return monthMaxDays[month];
	
                    return monthMaxDaysLeap[month];
                }
                else
                    return monthMaxDays[month];
            }

function createCalender(year, month, day)
            {
                // current Date
                var curDate = new Date();
                var curDay = curDate.getDate();
                var curMonth = curDate.getMonth();
                var curYear = getRealYear(curDate)

// if a date already exists, we calculate some values here
                if (!year)
                {
                    var year = curYear;
                    var month = curMonth;
                }

// first day of the month.
                var fristDayOfMonthObj = new Date(year, month, 1);
                var firstDayOfMonth = fristDayOfMonthObj.getDay();

continu		= true;
                firstRow	= true;
                var x	= 0;
                var d	= 0;
                var trs = []
                var ti = 0;
                while (d <= getDaysPerMonth(month, year))
                {
                    if (firstRow)
                    {
                        trs[ti] = document.createElement("TR");
                        if (firstDayOfMonth > 0)
                        {
                            while (x < firstDayOfMonth)
                            {
                                trs[ti].appendChild(document.createElement("TD"));
                                x++;
                            }
                        }
                        firstRow = false;
                        var d = 1;
                    }
                    if (x % 7 == 0)
                    {
                        ti++;
                        trs[ti] = document.createElement("TR");
                    }
                    if (day && d == day)
                    {
                        var setID = 'calenderChoosenDay';
                        var styleClass = 'choosenDay';
                        var setTitle = 'this day is currently selected';
                    }
                    else if (d == curDay && month == curMonth && year == curYear)
                    {
                        var setID = 'calenderToDay';
                        var styleClass = 'toDay';
                        var setTitle = 'this day today';
                    }
                    else
                    {
                        var setID = false;
                        var styleClass = 'normalDay';
                        var setTitle = false;
                    }
                    var td = document.createElement("TD");
                    td.className = styleClass;
                    if (setID)
                    {
                        td.id = setID;
                    }
                    if (setTitle)
                    {
                        td.title = setTitle;
                    }
                    td.onmouseover = new Function('highLiteDay(this)');
                    td.onmouseout = new Function('deHighLiteDay(this)');
                    if (targetEl)
                        td.onclick = new Function('pickDate('+year+', '+month+', '+d+')');
                    else
                        td.style.cursor = 'default';
                    td.appendChild(document.createTextNode(d));
                    trs[ti].appendChild(td);
                    x++;
                    d++;
                }
                return trs;
            }

function showCalender(elPos, tgtEl)
            {
                targetEl = false;

if (document.getElementById(tgtEl))
                {
                    targetEl = document.getElementById(tgtEl);
                }
                else
                {
                    if (document.forms[0].elements[tgtEl])
                    {
                        targetEl = document.forms[0].elements[tgtEl];
                    }
                }
                var calTable = document.getElementById('calenderTable');

var positions = [0,0];
                var positions = getParentOffset(elPos, positions);	
                calTable.style.left = positions[0]+'px';		
                calTable.style.top = positions[1]+'px';

calTable.style.display='block';

hideSelect(document.body, 1);
            }
            function showCalenderBody(trs)
            {
                var calTBody = document.getElementById('calender');
                while (calTBody.childNodes[0])
                {
                    calTBody.removeChild(calTBody.childNodes[0]);
                }
                for (var i in trs)
                {
                    calTBody.appendChild(trs[i]);
                }
            }
            function setYears(sy, ey)
            {
                // current Date
                var curDate = new Date();
                var curYear = getRealYear(curDate);
                if (sy)
                    startYear = curYear;
                if (ey)
                    endYear = curYear;
                document.getElementById('selectYear').options.length = 0;
                var j = 0;
                for (y=ey; y>=sy; y--)
                {
                    document.getElementById('selectYear')[j++] = new Option(y, y);
                }
            }
            function hideSelect(el, superTotal)
            {
                if (superTotal >= 100)
                {
                    return;
                }

var totalChilds = el.childNodes.length;
                for (var c=0; c<totalChilds; c++)
                {
                    var thisTag = el.childNodes[c];
                    if (thisTag.tagName == 'SELECT')
                    {
                        if (thisTag.id != 'selectMonth' && thisTag.id != 'selectYear')
                        {
                            var calenderEl = document.getElementById('calenderTable');
                            var positions = [0,0];
                            var positions = getParentOffset(thisTag, positions);	// nieuw
                            var thisLeft	= positions[0];
                            var thisRight	= positions[0] + thisTag.offsetWidth;
                            var thisTop	= positions[1];
                            var thisBottom	= positions[1] + thisTag.offsetHeight;
                            var calLeft	= calenderEl.offsetLeft;
                            var calRight	= calenderEl.offsetLeft + calenderEl.offsetWidth;
                            var calTop	= calenderEl.offsetTop;
                            var calBottom	= calenderEl.offsetTop + calenderEl.offsetHeight;

if (
                            (
                            /* check if it overlaps horizontally */
                            (thisLeft >= calLeft && thisLeft <= calRight)
                                ||
                                (thisRight <= calRight && thisRight >= calLeft)
                                ||
                                (thisLeft <= calLeft && thisRight >= calRight)
                        )
                                &&
                                (
                            /* check if it overlaps vertically */
                            (thisTop >= calTop && thisTop <= calBottom)
                                ||
                                (thisBottom <= calBottom && thisBottom >= calTop)
                                ||
                                (thisTop <= calTop && thisBottom >= calBottom)
                        )
                        )
                            {
                                hideSelectTags[hideSelectTags.length] = thisTag;
                                thisTag.style.display = 'none';
                            }
                        }

}
                    else if(thisTag.childNodes.length > 0)
                    {
                        hideSelect(thisTag, (superTotal+1));
                    }
                }
            }
            function closeCalender()
            {
                for (var i=0; i<hideSelectTags.length; i++)
                {
                    hideSelectTags[i].style.display = 'block';
                }
                hideSelectTags.length = 0;
                document.getElementById('calenderTable').style.display='none';
            }
            function highLiteDay(el)
            {
                el.className = 'hlDay';
            }
            function deHighLiteDay(el)
            {
                if (el.id == 'calenderToDay')
                    el.className = 'toDay';
                else if (el.id == 'calenderChoosenDay')
                    el.className = 'choosenDay';
                else
                    el.className = 'normalDay';
            }
            function pickDate(year, month, day)
            {
                month++;
                day	= day < 10 ? '0'+day : day;
                month	= month < 10 ? '0'+month : month;
                if (!targetEl)
                {
                    alert('target for date is not set yet');
                }
                else
                {
                    targetEl.value= day+'/'+month+'/'+year;
                    closeCalender();
                }
            }
            function getParentOffset(el, positions)
            {
                positions[0] += el.offsetLeft;
                positions[1] += el.offsetTop;
                if (el.offsetParent)
                    positions = getParentOffset(el.offsetParent, positions);
                return positions;
            }
            
            function detectItem(originalArray, itemToDetect) {
                var j = 0;
                while (j < originalArray.length) {
                    if (originalArray[j] == itemToDetect) {
                        return true;
                    } else { j++; }		
                }
                return false;
            }

//remove item (string or number) from an array
            function removeItem(originalArray, itemToRemove) {
                var j = 0;
                while (j < originalArray.length) {
                    //	alert(originalArray[j]);
                    if (originalArray[j] == itemToRemove) {
                        originalArray.splice(j, 1);
                    } else { j++; }
                }
                //	assert('hi');
                return originalArray;
            }

JSP code (I only post the related with calendar so we can focus on these)

</tr>
<table id="calenderTable">
                                <tbody id="calenderTableHead">
                                    <tr>
                                        <td colspan="4" align="center">
                                            <select onChange="showCalenderBody(createCalender(document.getElementById('selectYear').value,
                                                this.selectedIndex, false));" id="selectMonth">
                                                <option value="0">Jan</option>
                                                <option value="1">Feb</option>
                                                <option value="2">Mar</option>
                                                <option value="3">Apr</option>
                                                <option value="4">May</option>
                                                <option value="5">Jun</option>
                                                <option value="6">Jul</option>
                                                <option value="7">Aug</option>
                                                <option value="8">Sep</option>
                                                <option value="9">Oct</option>
                                                <option value="10">Nov</option>
                                                <option value="11">Dec</option>
                                            </select>
                                        </td>
                                        <td colspan="2" align="center">
                                            <select onChange="showCalenderBody(createCalender(this.value, 
                                                document.getElementById('selectMonth').selectedIndex, false));" id="selectYear">
                                            </select>
                                        </td>
                                        <td align="center">
                                            <a href="#" onClick="closeCalender();"><font color="#003333" size="+1">X</font></a>
                                        </td>
                                    </tr>
                                </tbody>
                                <tbody id="calenderTableDays">
                                    <tr style="">
                                        <td>Sun</td><td>Mon</td><td>Tue</td><td>Wed</td><td>Thu</td><td>Fri</td><td>Sat</td>
                                    </tr>
                                </tbody>
                                <tbody id="calender"></tbody>
                            </table>

From what i debug, function createCalender might be the key to do it. Cause it draws the date of month. But somehow I have no clue how to do it. Please someone helps me. Thanks in advances.

Done it by compare date in function pickDate