Security filter for GPO to a group of computers?

This should be an easy question, but we have a GPO that has a security filter on it to only apply to select computers.  With security filters in gpmc,  I know you can use AD security groups to apply to user accounts in those groups, but I tried that with computer accounts and it did not seem to work.  We had a Win2003 domain at that time and we just upgraded to win2008R2 domain and I was going to try again and wanted to see if anyone knows an easy way to apply a GPO with a Security filter to a group of computers.  We do not want to put those computers into a seperate OU and only target those OUs with the GPO.

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Dan Heim