They got zombies in my Call of Duty

And I'm totally okay with that

Yes as reported all across the web Call of Duty World at War has an unlockable Nazi Zombie Horde mode. Just finish the single player game to unlock this mode.

Here is a link at Digital Something and if you want some video check out Geeks of Doom.

It's a 4 player co-op level that only ends when you all die. You and your teammates are stuck inside a building trying to fend off these Nazi Zombies. You will earn money that you can use on weapons and items to build barricades to keep the zombies out.