esattamente cosa trovi difficile?
ti butto giu un esempio
codice:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>
<head>
<title></title>
<style type="text/css">
<!--

-->
</style>
<script language="JavaScript" type="text/javascript">
<!--
function disabilita(){
	var rifdiv=document.getElementById('box')
	var allTags=rifdiv.getElementsByTagName('*')
	for(var k=0;k<allTags.length;k++){
		var n=allTags[k].tagName.toLowerCase();
		if(n=='input' || n=='select'){
			if(allTags[k].id=="" || allTags[k].id.substr(0,7)!='no_dsb_'){
				allTags[k].disabled=true;
			}
		}
	}
}
//-->
</script>
</head>
<body>
disabilita
<div id="box">
<form>
<input type="text" value="blabla"><input type="text" id="no_dsb_testo" value="blabla">

<select>
<option>a</option>
<option>b</option>
<option>c</option>
</select>
<select id="no_dsb_select">
<option>a</option>
<option>b</option>
<option>c</option>
</select>
</form>
</div>
</body>
</html>