Limit to campus network, throttle to outside

On a campus or other internal network it would be nice to be able to go full speed (or a higher throttled speed) on the local net and possibly have access to the outside world through a few nodes and throttle that connection to another lower speed.

The client shouldn't try to connect to the outside world if I want to be just on the internal network.

Another possible set up would be to have one linux node that is terminal based that has a few outside connections and the internal nodes would connect to that one to reach the outside world.

That node could be VPN to the outside world so it can't be detected, or possibly connect through wireless on a different ethernet.

A dorm could use wireless to share resources between rooms and have a dedicated node that connects to the campus network at a lower speed to prevent it from becoming a problem.

There are lots of things we need on campus because of restrictions, please make this as flexible as possible.

If it was possible to compile a smaller more limited version that could be placed into a linux wireless router, such as a WRT54G with DD-WRT, that would help.