Two teams, red and blue. Red team = humans, blue team = zombies. Everyone starts out red except for 1 person who is the zombie. He uses the energy sword to kill reds, all the while the reds use shotguns and anything else in their arsenal to prevent themselves from being cut in half. Those who the zombie kills switch to the blue (zombie) team and join the original zombie in killing the reds (humans). This is continued until either A. Time runs out and red wins, or B. all reds are dead and thus zombies, and blue team wins.
Here are some screenshots of the map.




Download the map Zombies HERE
We need to organize a time for all of us to get online and have a large game of zombies, Halo 1 style, oldschool. Post some times that would be convenient for you guys. I'm up for pretty much whenever.