I have the following code which changes the background image of table cells when mouse over. It only seems to work in IE. I don't think it worked in Safari either.

function menuRollOver(tID)
{
	 tID.background="images/menu_highlight.gif";
}
 
function menuRollOut(tID)
{
	 tID.background="images/menu_normal.gif";
}

Some html for my table cell:

<td onmouseover="menuRollOver(this)" onmouseout="menuRollOut(this)"

Dont quote me but i think ie is a little less strict on interpretation of some css features than others. you might try background-image and see if it works. You may even have to code both, one for ie and one for firefox (seems like half my css is coding for different browsers! I even have an iefix.css file on half my sites!