windows server 2008 r2 how to define local administrator on each machine?

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http://serverfault.com – I need to get a little help in tuning my active directory. I would like to be able to give the right of 'local administrator' to a group of users already defined in AD. This in order not to have to log on each machine and assign local administrator rights one by one to each user needed. thank you (HowTos)