ciao, prova così... il filter alpha di IE è alquanto ricco di opzioni

codice:
<!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>
<style>
.IEopacity {
	filter: Alpha(Opacity=20, FinishOpacity=100, Style=2, StartX=100, StartY=100, FinishX=10, FinishY=10);
}
#id1 {
	position:absolute; 
 	left:10px; 
	top:18px; 
	width:323px; 
	height:241px; 
	/*z-index:1; */
	background-color:#3300FF;
}
</style>
</head>

<body>
<h1>TEST TEST TEST TEST TEST</h1>
<div id="id1" onmouseover="this.className='IEopacity';"></div>
</body>
</html>