I'd suggest running it the same way the monthly contests work. Kick it off with a first panel and then let people submit entries for a week or so, at which point they are put up to a popular vote and the winner becomes the next panel in the series. People get to choose not only on the basis of the art work but also on which direction they want the story to go.
I suspect something like this would appeal most strongly to traditional artists. The Poser guys could probably work with it, but anything CG is going to be a lot harder and more time consuming. Could make for some very interesting results.