When we are talking about Exchange 2007 Resource Mailboxes the Delegate feature becomes essential because the mailboxes defined as Delegate can approve meeting requests.
In order to define the Delegates in the resource mailboxes using Exchange Management Shell, we can use the following cmdlet:
Set-MailboxCalendarSettings <Resource Mailbox> -ResourceDelegates <Mailbox>
The second way to define a Resource delegate is using Outlook, in the current post we are going to use Outlook just to validate the new entry created by EMS. Just open the Resource Mailbox using the Outlook and check Delegates Tab out as shown below (To get there click on Tools / Options and Delegates tab).
To understand and configure approval process for a resource mailbox, you can use the following MS document: http://technet.microsoft.com/en-us/library/aa996338(EXCHG.80).aspx