The Zombie mode of Call of Duty: World at War is a sure hit for fans of zombie flicks. I know I am, I even read the Zombie Survival Guide book. The zombie mode will have up to four players playing co-op defending themselves against limitless waves of zombies. Kills will then be converted over for points that can be used to buy further upgrades and weapons. The Zombie mode for Call of Duty 5 is unlockable after completing the single player campaign first. You will also be able to unlock the co-op campaign mode after beating the single player.