Amatuer Tournaments

I have a quick question for anyone who can help. I want to hold a Halo Tournament at my local arts and events center in a very rural area. I am hoping to get a hold of an official representative to talk about the legalities of something like this. The last thing I want is to get a tournament together only to have a lawyer from Microsoft come and shut everything down for some reason I was unaware of. Anybody know who can help?