Need help blocking P2P traffic on network

Ok, here's the background. I work at a hotel resort, we just finished a project to hardwire all the units for internet access. The access part is done, now I need some help to figure out the best way to control what people are accessing in the network. Our biggest concern is P2P traffic which has proved to be a real pain in the butt. For this I plan to use a server for the network, Ubuntu is the one we have in mind. Now, here's the tough part, I need some ideas of what to use to kill that traffic. I know my way around Linux, but I've never actually worked on a server.

Please help.