I've been trying to find out how to do this without using a special function that somebody wrote. My problem is that on the main page I want to grab the post's image and specify a size (thumbnail in one place, large photo in the other). I thought that wp_get_attachment_image() might do the trick but I'm not having any luck with it.

Any help on what function I use to grab the post's image?

Here's the site that I'm working on: http://beacon.nwciowa.edu