oooh, I know, I know!
I have a whole world thought up for a pen and paper rpg I was making many moons ago. I considered making it into a web based mmo before, then went back to the hacking idea. I would be happy to let you use it as a theme (I would rather it get used in someone elses game than have it sitting mouldering away unused in my brain meats.)
Ive quite a bit of it worked out already (in my head, mind) but its still at the stage of being massively flexible, so anything about it that doesnt quite fit with your game can probably be easily altered to fit. Plus, I would be willing to help with any "flavour" type stuff (bits of story, npc character text, item description or whatever) that you might need.
I'd rather not blab this one out on a public board at the moment, but if you give me a yell over xfire or msn or something, I'll tell you more about it.
What I will tell you is that as far as I know, (and I would be very surprised to be proven wrong) its a pretty original idea. Certainly I cant think of any MMO's, web based or otherwise, that has an even similar theme.
Like I said, grab me on some form of messenger program or send me a PM or something, and I'll go over it with you. And feel free to tell me to jam the idea up my arse if you dont like it
EDIT: its kinda close to the nickface's idea, but even *more* unusual. Without just being wierd.