What you are looking to do is called NAT (Network Address Translation). In this case the specific setup is called 1-to-Many NAT meaning you have one external ip address (you school/dorm network connection) and any number of internal ones. You will also need some form of port forwarding to enable the traffic to reach the empeg. There are several products available for doing this on windows, one I know from the top of my head is WinGate (http://www.deerfield.com/products/wingate).
If you're running Linux, it's all built in and you just have to set it up (http://tldp.org/HOWTO/IP-Masquerade-HOWTO/index.html).

// Jonathan