You could possibly try to change the MAC address on your Xbox 360 to match the MAC address of your PC, but if the issue is because of MTU, I'm not sure it would do much. On a side note, which might be helpful to others, what I do to get a wireless router to work in my dorm room is first I "register" my Xbox 360 console on the network (they have an online form for this). Then, since the network gives dorm rooms static IP addresses (from what I've noticed, whenever I check my PC IP address in my dorm, it is the same), I copy down the IP address of my PC and the DNS servers, gateway, etc. Then, I go into my router settings and give it the MAC address of my Xbox 360, and assign it the static IP of my PC's IP address and enter in all the DNS, etc, that I recorded earlier. After all that, once I restart my PC, the setup is usually good to go.