Where I go to school, I only get one connection to the network as well. When you connect a computer to the network for the first time, you have to 'register' it to gain access to the network, and the Xbox doesn't have the ability to do that. I'm guessing your situation is similar. I just picked up a cheap Linksys router to split my connection and it did the trick for me. As far as connecting your computer to the 360, I don't have a clue. Personally, I'd just pick up a cheap router or switch.