Restrict a Specific User on Workstation from getting on the Internet & the Address my My Computer

Hi guys, we recently got a virus on our network from someone on the internet. the powers that be want the internet locked out for certain users on a workstation, however other users need access to the internet.

I am running Win Server 2K3 with XP Pro on 10 Workstations. How do i restrict a specific user not to be able access the internet. And also not to be able to use the Address bar on "My Computer" to access this internet.

I need this ASAP.

Thanks Alot!