Well, I can't give you EXACT instructions, but I can tell you how I think it would work in theory!
1. You could use javascript....a variation of Boomer's detailed image popup perhaps?
2. You could use the onClick function. I'm not sure how Smarty will interepret this, but the code in a 'normal' link would look something like this:
Code:
<a href="{ImagesDir}/imagename.jpg" onClick="window.open('{ImagesDir}/imagename.jpg','','scrollbars=no,resizable=no,
width=500,height=690,menubar=no,toolbar=no');return false;" target="_blank">
Again, I have not tried this, so it is just an idea. Maybe someone else can chime in here....