To access a series of cheats, you need to go to the main menu screen where you’re strapped into a chair in a T-Shirt.
Now, alternatively press the shoulder trigger buttons on your pad of choice (around five times each) to free yourself from the chair.
Walk over the computer screen on the far right. Now, access the Black Ops’ Central Intelligence Data screen and from here you can enter various cheat codes.
Below are a few of the codes found:-
DOA - Unlocks top-down shooter Dead Ops
3ARC INTEL - Unlocks all in-game intel
3ARC UNLOCK - Unlocks all Zombie Mode maps
ZORK - Unlocks a retro text adventure