User Access

Dears,
I have small size Network (LAN). I have windows 2000 Server Domain environment with Mail & Proxy Servers, the problem is this my all users have administrative Password/Rights of his own machine Questions as following:-

1. He cannot access the Mails & Internet when they are not Login with Domain? He can access only, when they will login with Domain User.
2. I don?t take from them his Administrative Password/Rights of his own machine

Thanks.

Faisal Khan