We're talking about The Cavegirls Present: Fight Like a Girl, the Halo 3 tournament where all the proceeds go to fight breast cancer. Taking place on October 20, the only requirements beyond owning a copy of the game, and having an Xbox Live Gold account, is forking over the $10 entry fee.
As an added bonus, part of the rules include a no-asshole policy: "trash talking, racial slurs, sexist remarks, and other insulting comments" can constitute a DQ. Helping out a good cause and insurance the people you're playing with aren't the normal Live plebes? Sounds good to us.