Chuck, If you look at
http://www.facesofwow.com/gallery/index.php you'll see that's the main cat's and
http://www.facesofwow.com/gallery/index.php?cat=2 becomes the sub cat with the tables.
As for the thumb, I'm meaning as say user a uploaded the last pic for cat a.. it would show that thumb then user h comes and uploads to cat a then user h's new pic becomes cat a's new thumbnail.