I've had the Wii for a while but just got Rock Band this Christmas. I was going to wait until I'd actually had a chance to play it before I passed along advice, but paying the bills is keeping me from having any fun.
In lieu of personal experience, though, I'll pass along what the salesman told my wife:a) Get Guitar Hero - start with the original.b) While he won't vouch 100% that it will work, Guitar Hero is claiming it's control can now be used for the Rock Band Games. (Rock Band could be making the same claim for all I know.)
I will say that the kids...okay "associates" in the games section will usually have some good advice on stuff like. If you go to a place like GameStop this is especially true so you may want to throw some questions out there at the store.
Let us know how it goes.