Web access system

[Tommy Moore]

Hi guys. I've been asked to setup a system for the company that charges 
users for access to the internet.
Basically what we have is a slow satellite link to the world and since 
bandwidth is expensive for us we thought of setting up a system that will 
charge users for access to the internet in 15 minute time slots.
What can I use to track this sort of thing and how do I control the access 
to make sure that the system doesn't get used unless the user is being 
billed for it.
The clients are win95 and win98 and the server is a RH 7.2 linux box.

Thanks for any suggestions you may have.

Tommy