An alternattive way to get links to the next and previous post?

I’m working on a photoblog and I have pretty much everything I need set up except the previous and next navigation. I don’t want just previous and next links but am rather going to use some image mapping to link to the previous page.

I’m shooting for the type of effect that can be found here: http://www.huddletogether.com/gallery/japan/index.php?id=2

I got the image map all set up but can’t figure out how to get the url’s for the next and previous page automatically. The posts_nav_link won’t work and neither will the previous_post tag because I’m trying to do this on the index.php in addition to the individual posts.

Any ideas?