I don't see why not, they would need to add your routers ip or mac address to their allowed list. Most board schools legacy machines our routed through c2k for their internet anyway.
Bill are you trying to setup a dual wan router/modem.
We were looking at setting up vlans in here so we could control our networked devices easier, but weve put it on hold for a while as we don't have the time to sit down and properly think it out.
We were going to set ours up like this:
Vlan1: Servers
Vlan2: Domain PC's
Vlan3: Printers
Vlan4: iPads
Vlan5: Staff Devices
Vlan6: Guest access(internet only)
The problem is getting them to talk to each other, its a lot of frigging about to get it setup right and we didn't have time, i think that will be a next summer job.