before I say anything, the important thing to remember is that the footer'll have to fit in with the layout - so you're either looking for a (horizontally) tiling image that fades from black at the top to... less black at the bottom, or you're looking at an enclosed and sharp-edged footer sitting in one of the corners. Either way.
There's really no maximum dimensions on it. DSW wants some banners in the footer, CF profile links are generally accepted, and a mention of myself at the bottom wouldn't be too much. So fit all of that in there, and you'll be set. I'm leaning towards having a tiling background fading to black at the top and a tiling footer fading at the bottom, by the way.
Oh, Matthew needed a test comic to get an idea of how big the comics will be so he could code the layout around it. I didn't want the comic to appear on the front page so I set it to update in 1990.