New Airport Time capsule on dorm network
Since you only have 1 IP address from the school, you need to make sure that your airport is setup in NAT mode, and not in bridged mode.  You'll need to make sure it's giving out DHCP addresses as well, and you may want to make sure it's not in a range used elsewhere on campus so that you don't run afoul of weird routing issues.  

I suggest the 172.16 range since it's rarely used by institutions in my experience, YMMV.

Let me know if this is helpful!