Only Lan not Internet

[ginzon]

Hi to all
OK plz be patient as u have to read a story size post....

My college has a proxy server...Own ISP....
There is a lab of which i m a member n we were warned by the Server guys for excessive downloads during college hours n stated that we r hogging up half of their bandwidth, but the scene is that we do not download during college hrs.
We either do it at morning 8am to 9am that too not much, as college starts at 9am, or after college hrs.
Practicals are conducted in those labs n people download movies over there n we r not always there to see whose doin wat...these are those guys bcoz of whom we r being screwed...
Is there a way so that we could allow them to use the domain only n not internet....
there are only 6 PC's wit internet now n the server guys may remove our PC's too, so plz help...
Domain should be accessible but not internet...
Solution for both Windows XP and Ubuntu plz as we have Systems with dual boot...

[Raymond]

Proxy servers supports authentication where the user will have to enter login data before they can use the internet.

[ginzon]

Yes n everybody has that so that they r accessible in the cyberlab n the domain...
I want them to just login on the machine to use intranet not Internet using their ID's...

[Raymond]

Like I said, if you're using Microsoft Proxy Server, you can set restriction that a user will need to enter username and password when the user launches internet explorer and tries to open a website. It has nothing to do with the domain login.

[ginzon]

Ok i didnt explain everything properly i guess....

Our Domain logins n internet usage logins r the same...
to login on the PC use r Login id same login id is applicable for internet....