Require Successful Login for Internet

Currently on our campus if a Windows 95 user hits 'Cancel' at the logon screen, the internet is still available. We would like to require a valid logon for any network activity. We are using NT 4.0 for our servers. DHCP assigns IP addresses.

Any ideas on how we can do this?

Use a System Policy to "Require Validation by Network for Windows Access" or modify the registry directly...
http://www.windows2000faq.com/Faq.cfm?FaqID=1832
http://www.regedit.com/detail/130.html

Thanks, I'll give it a try.