Image Rollover Buttons For Page Links

I’m using the Tarski template and I’ve set up my sidebar so that it only has page links in it. I want to turn those page links into rollover images. How do I do that? I don’t want to just have the links change color when I hover over them. I found a topic that had some code in it but I’m not sure where I would put it or in which .php file.

Any ideas? Thanks!