Instructions
Press the "Power" button on the PS3 to turn it on, then insert the "Modern Warfare" disc into the CD slot on the gaming system console.
Scroll to the "Modern Warfare 2" option under the "Game" menu in the XMB menu screen, then press the "X" button on the controller to load the game.
Select the "Multiplayer" option on the main game screen, then select the "Split Screen" option on the next screen that loads. The Split Screen Sign In screen will open. Choose which controller you want to use the God Mode in and press the "X" button to have that player enter the game.
Press the "L1" button on the controller while the game is playing to make the text entry screen appear, then use the "Left/Right" arrow buttons to navigate the on-screen keyboard.
Enter "devmap mak" into the entry screen, then press the "X" button. Enter "god" into the entry screen, then press the "X" button. You can then access the "God mode" with each of the other three controllers through these same steps.