yeah. this will be the first time I have tried it. one of the clothing options you can get for online play is a Zombie outfit. the game mode (player created, not official) goes something like this:
Team Deathmatch or free mode.
assuming 16 players, 6 are humans, 10 are zombies.
humans cannot use radar, are limited to light weapons, no cars.
zombies melee weapons only, can use radar, no cars.
I might be mistaken, but I think if a human is taken down by a zombie, they have to join the zombie team.
my assumption is that when all zombies are dead, or all humans switch to zombies, the game is over.
seems like it might be fun, given my fascination with all things living dead. I'm a little hazy on the rules right now.