calendar popup comes behind the modal window

[Sajin Balakrishnan]

I am using the following calendar
http://www.dynamicdrive.com/dynamicindex6/popcalendar.htm." target="_new" rel="nofollow">webpage
This calendar works proper in a simple form.But in a modal dialog it appers behing it.Whar could be the problem.

Modal dialog code

<div class="boxmod">
			  <table width="90%" border="0" cellspacing="1" cellpadding="5"  class="trialtable">
			   
                <tr>
			      <td>Start Date:</td>
			      <td><input name="txtCalFrm" type="text" id="txtCalFrm"  class="dtbox"/><a href="javascript:;"><img src="images/ico-dtpickr.gif" align="top" alt="Select Date" name="txtCalFrm" border="0" id="txtCalFrm" onclick="popUpCalendar(this, document.frm.txtCalFrm, 'dd-mmm-yyyy', 0, 0)" /></a></td>
		        </tr>
			    <tr>
			      <td>Due Date:</td>
			      <td><input name="txtCalFrm" type="text" id="txtCalFrm"  class="dtbox"/><a href="javascript:;"><img src="images/ico-dtpickr.gif" align="top" alt="Select Date" name="txtCalFrm" border="0" id="txtCalFrm" onclick="popUpCalendar(this, document.frm.txtCalFrm, 'dd-mmm-yyyy', 0, 0)" /></a></td>
		        </tr>
               
		      </table>
			  <br />
          
      </div>

[jhon masco]

What modal windows script are you using???