Yeah, I was about to say that demos of this game are either in stores (Gamestop, EB, etc) or hitting stores right about...now. I'm not sure if the demo has any multiplayer features; it might just be a single player demo of the game.
Speaking of which, there are a TON of PSP game demos hitting retail soon including NeoPets and I think Daxter, so keep your eyes peeled.
It would be nice if these demos were a) bundled onto one UMD a la Sony's Jampacks or, this is a wild thought, downloadable to memory sticks via either the internet or from retail PSP units. Nice dream, eh?