Internet Access Control is usually done through a Proxy/Firewall
Server. I run ISA and that works great for this. However, you should
be able to do it on your firewall by blocking access from the IP’s of
the machines.
The other way is to setup bogus "proxy settings" and then disable
the users ability to change them. That works great but ONLY for IE. It
won’t limit FTP or any other Browser like Mozilla (which can be
downloaded and run from any drive without installing into Windows)
The final way is to run xcacls.vbs as a startup script to remove the
permissions on the Internet Explorer Folder. I do that with Outlook
Express. Basically I reset to Admin and System = Full Control with
nothing else. http://support.microsoft.com/default.aspx?scid=kb;en-us;825751