Things You'll Need
Instructions
Insert the USB side of your PS2 to PS3 adapter into the PS3's USB port, which is on the front of the PS3 in the bottom left-hand corner.
Plug your PS2 Guitar Hero guitar into the guitar port of the PS2 to PS3 adapter. You will need a separate adapter for each instrument you plan to use.
Set the adapter to "Guitar Hero" when prompted. You'll now be able to use any of your PS2 Guitar Hero controllers with your PS3.