Instructions
Turn on the PS3 and wait for the system to load. Highlight and select "PlayStation Store" from the PlayStation 3 menu.
Highlight and select "Add On." Highlight "Search by Title." Use the on-screen keyboard to select "C." A list containing all games that start with "C" appears. Scroll through the list until you find "Call of Duty: Black Ops." This takes you to a page displaying all available downloads for the game.
Read through the titles of the downloadable mods while looking for any mention of zombies. Mods are listed for both the main game and mods for the "Nazi Zombie" addition. Select a mod to read its details. Click "Download" when you find the mod you want added to your game. Select your PS3 hard drive as the storage device, and the download begins. Wait for the download to finish, then restart the system and start your game.