GH:WT is compatible with RB2, and vice-versa. but other versions aren't, although there are a couple of exceptions that i can't rememeber right now. WT and RB2 are the fully compatible ones though.
that could be alot more fun than gh guitar, but i think ill just sick with the drums. But, i think thats gonna come pretty expensive? if i got the point that game is played by a real guitar, and those cost pretty damn much