An NMAP Scan on qq.com flags it as being Apache HTTPD. From my log: "PORT STATE SERVICE VERSION 80/tcp open http Apache httpd |_ HTML title: 302 Found"

I have been a part of a group that pulled off a few public lan parties. We had around 60 to 70 people at each one and never had a single problem with theft. Most of our attendees didn't stray very far from their rigs. We did require that people register in advance or when they arrived so we knew their name and handle. I would recommend you require people to be 18+ or be with someone who is. When they register, have them sign a disclaimer if you are really worried about a law suit.