[Black Ops] Getting All the maps and Secret Achievement

When you start up your game, you should appear at a Start Menu. Press start and begin.

You are in a interrogation room.
Double tap on the triggers to break free. (L1 and L2)
Walk around the room until you see the computer.
Hold (X) to access it.
Type in these codes:
3arc Unlock - Unlock all Zombie Maps (not from WaW)
Zork - Secret Achievement
3arc Intel - Unlock All intel (will not be able to earn Intel Achievements)