In Exchange 2007, they have finally done resources correct. Using Powershell, you can define a mailbox specifically as a conference room, laptop, projector or other resource. As a resource it will appear differently in Outlook 2007 and OWA. These resources can be defined to automagically accept meeting requests using specific permissions on these resources. No longer will you need to use the flaky AAA as in Exchange 2003.
The attached script is my very detailed, all-in-one convert a standard/migrated mailbox to a conference room resource in Exchange 2007.