Instructions
Rapidly press the right and left trigger buttons on the game controller at the "Black Ops" starting screen. Your character will break the straps confining him to the chair and stand up.
Move to the computer in the back of the room, and press "X." This will bring up a computer monitor and an onscreen keyboard.
Enter the code "3ARC UNLOCK" into the computer. This will unlock all non-downloadable content zombie maps. Alternatively, you can unlock these maps by beating the "Black Ops" single-player campaign.
Move back to the chair, and press "X" to sit back down. This will turn the monitor with the main menu options back on.
Select "Zombies" from the main menu, then choose the network option that works best for you.
Create or choose a game from the games lobby list.
Start the game once two other players have joined the match.