Archived from groups: microsoft.public.win2000.active_directory (More info?)
The easiest way to do this is either via Restricted Groups (GPO) or a simple
startup script that uses the net localgroup command. However, you could
also write something in VBScript that would go off and do this on a per
machine basis if you so wanted to...
The command for the batch file that would be the startup script would be:
net localgroup administrators DOMAIN\UserName /add