IM, huh?
What exactly does that entail? Because, if you're going to be doing a lot of sending of information over the internet, using voice chat / video conferencing etc., you might need a lot of ports opened up anyway. Usually, the first people you run into aren't going to know what you're talking about, try to get up the chain somehow.
Ultimately, you, or someone who knows what they're doing, are going to need access to the dorm's firewall setup. That's where the firewall's going to have to be opened up for you to get out and play...
Good luck...