*Enable multi-users to connect to the Internet through single dial-up networking.
* Track Internet usage of users hosted on Windows NT server.
* Maintain user account balances using database files while enabling a single location to be kept for users in each domain.
* Work with multiple/trusted domains.
* Ability to configure popup windows that appear after Internet jobs. Windows should include amount of money or time left and used at workstations. They should also allow users to enter client codes and job numbers, usernames and passwords for shared logon Internet accounting and network passwords for Internet security.
* Generate statistical reports on Internet activity by user, group or client code.
* Rules based Internet for load balancing based on maximum and minimum time usage where jobs can be allowed or disallowed depending on time allocated or used.
* Individual prices can be set for different types of users? (student and staff) jobs can be discarded when using an invalid allocated time.
* Utilities for users to check their own account balances versus amount of money or time left and used. It should also be juicy or add more Internet usage time to their accounts.
* It should have a proxy server application.
* It should have Internet sharing.
* It should have stealth firewall site filtering.
* It should have site caching.
* It should have VPN and NAT capabilities.
I don't know of any application that meets all of your needs. I haven't reviewed competitive offerings of this type recently. All that I'm familiar with is Microsoft's Internet Security and Acceleration server. You can find more information at http://www.microsoft.com/ISAServer/.