prevent unauthorized macs from internet

Set a specific DENY on the Access List on either the router or the Firewall.

A good book for Cisco is here with sample chapter:
http://www.oreilly.com/catalog/cisrtlist/chapter/ch05.html

If you don't have the options suggested in Answer 1, you could install a Proxy Server and setup your PCs to be only allowed access to the internet via that proxy server. Within the proxy Server you can set the user who are allowed to do what.

If you use 200x as your DHCP server, you can assign your Windows machines a DHCP Class. In DHCP, you specify a gateway (router) address to that class. Machines with no DHCP Class or another class will not get the router address...and no Internet.

and now for the links...(remember to remove spaces that may get added)

http://support.microsoft.com/default.aspx?scid=kb;en-us;235272
http://support.microsoft.com/kb/240247/EN-US/

Cheers!
~Sean

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