You've seen the videos of custom gameplay. Now learn how to do it yourself. Bungie left a loophole which allows 8 players in one party and 1 in another to access the custom game lobby in Halo 3 beta. Pistols, plasma swords, and even a setting to adjust the active camoflauge is available.
im deffinatly going to be trying this before the beta ends.
Less then 7days left!