Is there a free mmorpg that you can be the zombie

Well if you are looking to roleplay a zombie there are many. Like MagicDuel.com, in which you create your character in terms of your actions (the role you get). In it you can even create an avatar for your character and I'm sure it can be a zombie.

If you are looking for a specific zombie game, I don't recall playing anything like, in most you kill the zombie :)