Determine if mailbox is a 'resource' or user

When you create an appointment programmatically you can specify the type for
each recipient (olResource, olRequired etc).

Is there a way of finding out if a mailbox is a resource like a room or
piece of equipment? I noticed that Exchange 2007 has new mailbox types
specifically for rooms and equipment - does this make a difference in
retrieving mailbox properties?

Thanks, Tad