Didn't you have another thread on this somewhere on here? Anyways having the link does help I can see the code is some JavaScript added to the template. It does not look like they are using any type of external JavaScript file as its not linked in the headerinclude template. The code that is making this happen I believe is this:
Code:
<h3 class="threadtitle">
<a class="title" href="threads/808351-PP-Modeling-Emma-Model-Set-11" id="thread_title_808351" title="" onmouseover="return overlib('<div><nobr><img src="http://main.imgclick.net/i/00210/jbn2lelzvxei_t.jpg" style="border: 1px solid #731D1D; max-height: 160px; max-width: 160px; box-shadow: 0px 0px 20px #AAAAAA; "> <img src="http://main.imgclick.net/i/00210/aihpu8kau0fb_t.jpg" style="border: 1px solid #731D1D; max-height: 160px; max-width: 160px; box-shadow: 0px 0px 20px #AAAAAA; "> <img src="http://main.imgclick.net/i/00210/5fjj3xad90h2_t.jpg" style="border: 1px solid #731D1D; max-height: 160px; max-width: 160px; box-shadow: 0px 0px 20px #AAAAAA; "> <img src="http://main.imgclick.net/i/00210/tw8wueg8eg7z_t.jpg" style="border: 1px solid #731D1D; max-height: 160px; max-width: 160px; box-shadow: 0px 0px 20px #AAAAAA; "> </nobr></div>');" onmouseout="return nd();javascript:void(0)">[PP-Modeling] Emma Model - Set 11</a>
</h3>
It mainly has to do with the onmouseover command in JavaScript, but I don't hand code JavaScript from scratch so I'm not sure what you would put nad how in the template to make it right.
For obvious reasons you cannot use the exact code that I found from the view source page, but perhaps this will help you know what JavaScript to use if you are good with that sort of thing or it may help someone else help you make your site do as you want it to.