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 :)
You can try the links mentioned below.
There are quite a few completely free MMORPG's out there. Just a few of them are: Windslayer, Grand Fantasia, and Secret of the Solstice.
A free-to-play MMORPG.
Yes it is.
Flyff
aqworldcom is best mmorpg /w changeble characters
yes all you have to do is download it
Runescape
runescape.com battleon.com pawngame.com
Maple Story
the biggest game is WARROCK and its free and fun its a mmorpg
If you are referring to the fantasy MMORPG "Warrior Epic", then yes it is free