Interesting, cuz I was looking into the same thing.
Your best bet would be to have this in a spot thats really populated with teens, often - like a MALL.
We are thinking of starting with 20 pc's.... Rent out special joysticks/mice/etc... maybe even sell custom gaming rigs.
Anyways... if you need good lan gaming advice whether its for a party or a permanent place, check out
http://lanparty.com
Any ideas on what games you wanna host?