In Exchange 2007 you can use the following command to setup a Resource Mailbox to automatically book calendar appointments:
Set-MailboxCalendarSettings -Identity "RoomName" -AutomateProcessing AutoAccept
What about if you don’t want it to automatically book. Instead you want the meeting request to go to a delegate (or delegates) who then can approve or deny the request. You can use the following command:
Set-MailboxCalendarSettings -Identity "RoomName" -AutomateProcessing AutoAccept -ResourceDelegates "DelegateName" -AllBookInPolicy:$false -AllRequestInPolicy:$true
The theory is bascially the same in Exchange 2010 however all of these properties can be set in the Exchange Management Console under the mailbox properties.
The following article in the Microsoft Exchange Team Blog has more details on resource mailboxes: