Launch the game, click the Start button, when the options comes to select Campaign, Multiplayer, instead repeatedly press R2+L2 (RT+LT on XBox), you should remove the shackles (whilst also earning a trophy).
Next go and find the computer and use it. It will ask for a code on the DOS prompt, input the following:
3ARC UNLOCK - this will unlock the Zombie Map called "FIVE" featuring JFK, Castro & Co
DOA - this will unlock the Dead Ops Arcade minigame
ZORK - this will unlock Zork, a textbased adventure game
For those who are having a blonde moment, heres a vid tutorial as chri1143 mentioned in the forum: http://gamerant.com/call-of-duty-black-ops-zork-dyce-51858/
I have tried and verified all 3 working on the PS3, am assuming should also work on XBox by pressing the bottom two trigger buttons.
Those who were already considering buying Zork or DOA, dont miss your opportunity to get a free copy of BlackOps with it!
So Lock n Load.... :j