HOTFIX: Appointments that are sent between different Exchange Server organizations may be incorrect by one hour when one of the organizations is in the Western Australia time zone
Yep, I've been hit by this one :o(
Daylight saving time (DST) was introduced to Western Australia for a three-year trial period that started December 3, 2006. The Microsoft Exchange Server 2003 Collaboration Data Objects (CDO) tables and Microsoft Office Outlook Web Access tables do not contain updated DST transition times for the Western Australia time zone if this hotfix is not installed.
You must have Microsoft Exchange Server 2003 Service Pack 2 (SP2) installed before you apply this hotfix. You may have to restart the passive node in a clustered environment when you apply this hotfix.
http://support.microsoft.com/default.aspx/kb/929895