Instructions
Look at the bottom of the PS3 console. Make note of the serial code. It will begin with "CECH".
Determine if your PS3 model is backward compatible. The three serial codes that have backward compatibility are "CECHA01," "CECHB01" and "CECHE01." They are the 60 GB, 20 GB and 80 GB consoles.
Place the PS2 game disc in the PS3 game slot, just as you would with a PS3 game disc. The console will read the disc and start the game.