I've never played anybodies custom game mode on Far Cry 2.
I was playing on the 360 the other day and somebody had "Every" zombie map from every FPS game I know of that has a zombie map re-made in the editor.  This game can be up to 9 people.  Here are the rules.

Far Cry 2 Zombies:

9 player max, 1 person on the human team (pistol) and the rest on the zombie team (machetes)
For the first 10 kills:  the human is only allowed to use the pistol and the zombies aren't allowed to run
After (if) 10 kills is accomplished then the person who killed him is the human the next round.

Make sure you set the game so if the human team dies once, the round is over.

I'm not really into the zombie modes on any of these games they are actually from, but this mode was quite a fun change of pace for Far Cry 2.