Instructions
Turn on your PS3 and two controllers and then insert the game disc for the cooperative (two-player) game.
Choose the "PlayStation Network" option from the PS3 main menu and select "Sign In."
Enter in your PlayStation Network credentials (email and password) and press the "Sign In" button.
Initialize the cooperative game on your PS3 console and wait for it to load. Once you get to the main menu of the game, select the "Cooperative" or "Two Players" option. You will now be prompted to sign in to another profile.
Pick up your second PS3 controller and follow the prompts to sign in to the second PlayStation Network profile. You may now play the game with both PlayStation Network profiles.