How to unlock all the zombie maps in black ops?

I had kino der toten,five and dead ops arcade but still have one more map that need unlock. But I dont know how to unlock it.I need some help please. ThanksHow to unlock all the zombie maps in black ops?
There are only three maps that come with every version of the game, however there are four more maps that came as a download code with the Hardened and Prestige Editions. More specifically those four maps were the four for Call of Duty: World at War.

Edit: What Dinmagic says will unlock the 3 maps that come with Black Ops, in addition to being able to choose any mission from the campaign without having to play there first. It doesn't unlock the "classic" maps from World at War.How to unlock all the zombie maps in black ops?
On the Main Menu, alternately tap RIGHT and LEFT triggers (or hold the Space bar on a keyboard). After a bit, you'll stand up. Leave your seat and examine the back wall. A small black and white computer terminal can be found here. Approach it and it will ask for a password. Type in "DISK" then enter "3ARC UNLOCK" using the on-screen keyboard in the "Central Intelligence Agency Data System."



For some reason it didn't let me put any cheat codes unless I typed in "DISK" first.