Here's what I have:
In the <head> tag
<script type="text/javascript" src="prototype.js"></script>
<script type="text/javascript" src="scriptaculous.js?load=effects,builder"></script>
<script type="text/javascript" src="lightbox.js"></script>
<link rel="stylesheet" href="CSS/lightbox.css" type="text/css" media="screen" />
Then using it within a <map> and <area> tag:
<area shape="rect" coords="4,471,131,567" href="My.jpg" rel="lytebox" title="My Title"/>
The .js files are in the root and the .css file is in a css sub directory. The Lightbox image files are in an image sub directory.
As mentioned it works fine with IE but the screen dims but the image never opens with Mozilla.