1. Security filtering using GPMC

You have to install the GPMC for 2003 but in 2008 GPMC is available in any DC.

Remove the Authenticated users and add a  security group, find the screenshot for the same.



See the below links for implemainting  the Security filtering. You will get the step by step infomation with screenshots.

http://www.windowsnetworking.com/articles_tutorials/group-policy-security-filtering.html
http://technet.microsoft.com/en-us/library/cc781988(WS.10).aspx

2. Another way for GPO exclution.
http://social.technet.microsoft.com/wiki/contents/articles/exclusion-for-a-group-policy-object.aspx

3. Also you can use "Item lebel targetting" for GPO exclution.
______________________________________________________________________
GPO Troubleshooting

Also you can use the ADM/ADMX for GPO related issues (GPO DEBUG LOGGING).

http://www.gpoguy.com/FreeTools/FreeToolsLibrary/tabid/67/agentType/View/PropertyID/85/Default.aspx

http://www.gpoguy.com/FreeTools/FreeToolsLibrary/tabid/67/agentType/View/PropertyID/84/Default.aspx Use this tool for registry key change.

http://www.gpoguy.com/FreeTools/FreeToolsLibrary/tabid/67/agentType/View/PropertyID/87/Default.aspx 

I have tested all the above tools and all are working fine.