Or you could try something like tGA. I've developed a lot as a writer from playing tGA, although I still tend to write so much plot that the actual game never gets anywhere near caught up.
Some of my funniest material has been at tGA. We've tried to do something similar here at EoFF in the past (Magestar and I think a couple of other ones that lasted up to a week) but it never took off. We also tried it at GHF, but the only thing I remember about it was the awful sex scene I wrote, hoping that it would turn into an in-joke.
EDIT: Actually, it hasn't been done here in a while, so I'm going to write up a proposal in the Writer's Corner forum.Sod that, I took one look at the RP subforum and ran for my life. So many one-post and one-reply threads. There's no way EoFF could ever support a proper collaborative attempt. Besides, I've got nothing funny.