It's the new name for the RPG, they aren't multiplayer gamebooks as such, it's just the system is very rules light to let you do what you are doing just now with the MSN game, but with multiple people say... so you could weave stories straight from the gamebooks, or games to players with the gamebook characters without missing a beat andf without it causing a disconnect in flow
Its going to be pretty good as far as I can tell. The only buzzkill so far is that we will have to wait a couple of months to get rules for classes other than the Kai Lord. That kinda sucks, but oh well.
I bought the Multiplayer book from Amazon. I seems like it would be fun, but I kind of liked the details of the d20 RPG. Looking forward to the sourcebooks though!!! I guess you could take the classes from the RPG and adapt them to the multiplayer rules.