From IGN: "If you plan on picking up a PlayStation 3 anytime soon and are worried about the dent that the system and its peripherals will put in your wallet, you may want to consider picking up some USB adapters for the PS2's Dual Shock 2 controller. These relatively cheap adapters are made for using a Dual Shock 2 on a PC, but they seem to work quite well with every PlayStation 3 game that we've tried. You need to switch on the analog button when you plug them in and they're missing the PlayStation button that brings up the Cross Media Bar, but other than that they seem perfectly functional.
With that, we assumed that Guitar Hero and its sequel would work perfectly well on the PlayStation 3. Unfortunately, that doesn't seem to be the case. When you pop in a PS2 or PSone game, you're prompted to tap the PlayStation button on the controller. For what reason, we're not sure, but as Guitar Hero's SG controller doesn't have this button, you can't actually activate it. You also can't quick-swap from one controller to another as the second part of the problem lies in that you need to turn on analog control, but again, the SG guitar doesn't have an on/off button for analog play."