IE6 and IE7 in quirks mode don’t support :hover pseudoclass for non-anchor (<a>) elements.

This little css trick can workaround the problem (example on a <tr> element):

tr { background: #ffffff; hover:expression(this.onmouseover=new Function("this.style.background='#ff0000';"),this.onmouseout=new Function("this.style.background='#ffffff';")); }
tr:hover { background:#ff0000; }

First line define background color for generic <tr> element and implement hover behaviour for IE, second line catch hover for standard-compliant browsers.