You're right that local accounts don't apply, but Richard was not suggesting
He was suggesting that you add the user's DOMAIN account to the
administrators group on the LOCAL PC.
If you want to allow any user to be an administrator of a particular machine
only while logged in at the console, you could add the group called
INTERACTIVE to the administrators group. This will give admin access at the
local machine, but not over the network.
Bear in mind that you are allowing your users to look at and modify the
cached profile directories of other users if you do this. If Power User is
sufficient rights, use that instead.
The Group Policy feature you're thinking of is called Restricted Groups. Do
a search on support.microsoft.com for this and you'll find some good