Windows Vista has already shipped with the appropriate changes, but Windows XP Service Pack 2, Windows Server 2003 and Windows Server 2003 SP1 (as well as several other Windows-derived products) all need to be updated.
These changes have been published as updates for Windows, as described in Knowledge Base article 931836, February 2007 cumulative time zone update for Microsoft Windows operating systems.
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\Current Version\Time Zones\ Sounds like the Microsoft time zone patch did not take, or had issues.
If you're interested, you can create a GPO of that registry key (from your highest Windows version that is fully patched) and apply it to your Windows computers.
While I can't spare you the trouble of having to read the document for yourself, here is a synopsis of the important issues as they pertain to Exchange Server and Microsoft Outlook.
This works best when you have a small and technically savvy set of users who can get hands-on guidance for how to use the tool, since it allows for much more selective changes to be made.
In most every case, you'll need to apply the update for Daylight Saving Time changes in 2007 for Exchange 2003 Service Pack 2, which addresses the way Exchange Server handles time zones.
But what about Microsoft Outlook appointments that fall within the affected time zones?
(Of course, this doesn't count changes to events that have been scheduled for future years.) Microsoft's response to this whole situation has been somewhat scattershot, since there's really no one utility a person can download to fix everything at once.
Redmond's approach has been to deal with the problem in three discrete ways: the operating system level, the individual product level, and the application data level.
Check the following registry key on the clients that aren't updating to ensure they have the correct registry values.