Mailboxes created for conference rooms (on Exchange 2007 Recipient Type : Room Mailbox) by default has disabled auto accept for calendar appointments. That causes issue when people trying to book room as all appointments show as tentative and manual interaction/accept is required. In order to streamline process and make it more handy for people (in case nobody is assigned to control room bookings) you can enable auto accept feature, so all appointments will be accepted automatically. To do that use PowerShell:

[PS] C:>Set-MailboxCalendarSettings -Identity "ConfRoom"

Whole command should be in one line.  In example it is broken down into 2 lines due to SyntaxHighlighter limitations.