<html>
<style>
p {
border:1px solid red;
max-width:30em;
width:expression(
document.body.clientWidth > (500/12) *
parseInt(document.body.currentStyle.fontSize)?
"30em":
"auto" );
}
</style>
<body>
<p>
[alot of text]
</p>
</body>
</html>
reference : http://www.svendtofte.com/code/max_width_in_ie/