First published on TECHNET on Mar 07, 2007

Q: I just saw reference to a new hotfix for Outlook that I had not seen discussed before nor did I think was needed beyond the XP fix – – I'm confused. (we won't be applying 926666)
A: This hotfix is for Outlook 2003, rather than Exchange.  KB 926666 is for Exchange 2003 SP2.  KB 931978 is the Exchange 2003 SP1 version.  While Outlook is mostly dependant on the underlying OS for time zone information, it also has some components that contain their own logic. The version of the Collaboration Data Objects (Cdo.dll) file that is included with Outlook 2003 currently does not comply with daylight saving time (DST) starting in the year 2007. If this version of the Cdo.dll file is used to create, modify, or accept appointments, the appointments may be off by one hour.

So, you should apply the appropriate Exchange hotfix to your server, and also apply this hotfix to any Outlook 2003 clients that you have.  This is in addition to deploying the OS patch (931836) to all clients and servers.