I've played the entire campaign, and adjusted some of the settings in multilayer. It still wont show up. Anything else I could try? If nothing else, I can just wait till I actually buy the game (which I definitely will) but it would be nice to be able to play zombies..
One more note, after playing through the campaign, after the final credits, it goes directly into zombies. Had I known I wouldn't be able to get back... I would have stuck around a bit longer.
EDIT: I found a fix online for it. Nevermind.