all right here goes...

Samba server setup for a at least 12 users so far....about 8 pc's that connect up with different users using them, each logon with there own account, all win-xp pc's...This side of things is fine...
4 x users have full internet access, so far i have bridged the server as a gateway...
but all other users will only have access to one web site when they logged on...
admin done by ssh from my machine at home so will secure that once i get the restrictions in place...
i need to close the gateway so only 4 accounts have full net access and all others have access to this one training site...the pc's are shared so i cant block ip's, have to have some method that allows usernames access and allows all pc's full access when those that have it use them...

I have a few ideas but dont want to waste too much time searching...
anybody who has done this and can give me a guide that works, i shall be grateful...

Server has two ethernet cards, eth0 is lan and eth1 is the internet..
distro is ubuntu breezy 5.10 server install(minimal)...no graphics, so dont give me any click and flicks...all from shell...
i was thinking a firewall, but this dont make real sense, and i cant seem to find what i want with squid, plus i dont know squid very well at all...

cheers