What if you use the
<?php wp_link_pages('pagelink=<img src="wp-content/themes/brink/images/button_%.gif" />%') ?>
I'm thinking that will call for
button_1.gif for the first page,
button_2.gif for the second page, and so on. Then you just change the names of your GIFs accordingly. Give that a shot. And look at the code to see if any part of that IMG tag renders. The image might not show because of an incorrect URL to the image, but just make sure the code is even working as it's supposed to. I don't use pages at all so I've no way to test this myself.
And if you're going to bump, try to at least give an update on what you've tried to do since you last posted, things you've read, experiments that failed, etc. That'll help us know what you've already tried and tell us that you aren't just sitting on your hands in the meantime.