http://chrispoole.com/scripts/javasc...mage-rollover/
This works great for me in the past. Up the js file(possibly to your clientscript directory). Then add
PHP Code:
<script type="text/javascript" src="dom_image_rollover_hover.js"></script>
to the headinclude. It may also work by just using it in the header template itself. Been awhile since i used it but if you need help drop me a pm.