I'm in a college dorm, and trying to connect to Xbox live...?

So, I'm in a dorm at UNC in Greeley Colorado, if that helps, and I'm trying to get onto xbox live using the ethernet cable and plug that I use for my computer. I don't need to have xbox live and internet on my computer at the same time, and I don't need the live to be uber fast, all I'm going to really use it for is content download. (I've heard there's a free kind of live that pretty much lets you do just that. Confirmation?) The network adaptor, IP address, and DNS all check out, but it always Fails at MTU. I don't even know what the hell that is, or if I'm just wasting my time and need to buy some inhumanely overpriced crap from the cheap s at Microsoft. Help... please...