Populating one Drop Menus from another several levels deep

I've always avoided java script and stuck to php, but now I need to build a cascading menu selection where selecting one menu item populates the next menu box, and that menu choices populate yet another menu. I have no hair left so Im hoping someone can tell me what Im doing wrong here:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Cascade Dynamic Menu Document</title>
</head>

<body>

<form name="myform"><div align="center">
<select name="optone" size="1"
onchange="setOptions(document.myform.optone.options
[document.myform.optone.selectedIndex].value);">
<option value=" " selected="selected">Choose Valve Size</option>
<option value="1">1 Inch Valve</option>
<option value="2">1 1/4 Inch Valve</option>
<option value="3">1 1/2 Iinch Valve</option>
</select>

<option value=" " selected="selected">Please select one of the options above first</option>
</select>

<select name="optthree" size="1">
<option value=" " selected="selected">Please select one of the options above first</option>
</select>
<input type="button" name="go" value="Value Selected" >
</div></form>

Welcome to the Ranch!

Here are a few tips to help you get better, faster answers:

Post in the correct forum. JavaScript is not Java. I've moved this to the HTML/JavaScript forum for you.

Format your code. You used code tags to post your code (good job!), but your formatting and indentation is really wonky which makes the code hard to read. Easy to read code means more and better answers.

Be explicit about what's happening. Just saying that it doesn't work doesn't give us much traction to help you.

Cheers and welcome.