When you use Microsoft Office Outlook 2007 to open your mailbox located on an Exchange Server 2007, Outlook will use the Autodiscover Web service to retrieve the URL to be used when retrieving Free/Busy information to access the Availability Service offered by a Client Access Server. You can however force a Microsoft Office Outlook 2007 client to retrieve and publish Free/Busy to a system public folder by adding the following registry DWORD_value:
Key: HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Options\Calendar
Name: UseLegacyFB
Value: 1
After restarting Microsoft Office Outlook 2007, Outlook will still receive a URL from the Autodiscover Web Service for Availability Service, but will retrieve and publish Free/Busy data to a system Public Folder.