If your ever bored with matchmaking, you can set up your own little gametypes with the Private Match selection. Here's how to play zombies with Call of Duty 4

[edit] Steps

Get a party of about six or more people and go into a private match.
Set the game up by making it Team Deathmatch and set the time limit for 30 minutes with an unlimited amount of score.
Make sure that all zombies only use the knife and their only stun and nothing else.
Have zombies have a class set up to include a scorpion with extreme conditioning to make them run faster.
Switch to the zombie team when you are killed.
Humans may use any weapon at their disposal including air support.
Change the gametype to hardcore, and headshots only for an increased challenge.
Find a good spot to defend, if you want to be a lone wolf hide in a spot you can defend and move when a zombie attacks you, the main group of humans may stick together in one spot and attract all of the attention.

[edit] Tips

Zombies may also have dead silence to increase their chances of eliminating a human
Humans should carry bandolier or claymores to last a fair amount of time.
Overkill is another recommended perk for humans. Not only can you have two guns for more ammo, you can carry a skorpion just how you like it to live off the zombie's ammo.
When you are the last one left either hide or pick a good defense spot and hold your ground untill the time limit.
Use your knife and your wits when faced with a zombie horde with no ammo.
Do not use any glitches, this ruins the fun of the game and may get you booted from the party.
The first one to be killed is the next zombie and if you are in a large party include two zombies at start then the next two people are zombies etc.