Instructions
Check the cross-controller compatibility between the model of the "Guitar Hero" guitar, the PlayStation 3 game, and the "Rock Band" version. The "Rock Band" website offers a compatibility chart. Some "Guitar Hero" guitars will not work.
Turn on the PS3, insert the "Rock Band" game and also plug the "Guitar Hero" guitar controller into the USB port on the PS3.
Start the "Rock Band" game and you should be able to play normally with the "Guitar Hero" guitar, for the game will recognize it.