Here's an idea for people who want to mix things up with their friends in a private match and are tired of normal game modes. I call it CoD Zombies, although this title is probably no longer appropriate due to World at War's zombie mode. Nevertheless, here it is.
 
- Set game mode to Team Deathmatch .
- Headshots only, no killstreaks, no radar, no friendly fire, third-person mode.
- Pick a smaller map, for MW2 I suggest something like Favela or Terminal.
 
Now, normally I'd say make the teams 3vs1 but unfortunately, MW2 has completely disabled this option forcing balanced teams. CoD4 and CoD: WaW both allow 3vs1 matches though. Anyways, one team will be the survivor, the other, the zombies. The survivor is allowed to use everything except his knife and the Marathon perk. The zombies can only use knives and nightvision. Generally, it's best if the survivor is the worst player or one who is least familiar with the map. Also, they cannot go on a spot in which the zombies cannot reach without help of a ladder.
 
It's actually super fun. Try it out.

I shall give it a go sometime.

it would be way cooler if somehow you could set one team to only be able to use knives but they require headshots to be killed

Too many rules.

" @Maxszy: I do have it, but it doesn't have four-player splitscreen, where this idea is most useful. "

can you even use night vision in multiplayer? i haven't seen it. or maybe that's just me.