Deny access to Internet to a single user

Hello. I need help. How to deny access to internet to a specific user on a specific machine.

This is the configuration:

Internet DSL router is conected to ethernet hub.
Everyone connects to same hub.
Everyone has static IP.
No proxy
Windows Server 2003 on Domain Server.
Machine runs windows 2000 pro.
Other users of same machine must have access to internet.

Thanks for your help.