Hi Marcel, there are loads of ways to do this in css or js. You are likely to have to over come issues with ie's problems with png transparency and/or lack of support for hover on anything other than a tags. Which one you pick might depend on the exact effect you are after.
Since this is Qcodo forum though, what about the QImageRollover ?
$this->marcel=new QImageRollover($this);
$this->marcel->ImageStandard='images/left.jpg';
$this->marcel->ImageHover='images/right.jpg';
$this->marcel->LinkUrl='page.php';
and in the template:
<?php $this->marcel->Render(); ?>
Ive just tried it now and it worked on Firefox and ie 6.