Step by step run of the Exchange Calendar Update Configuration Tool (MSExTMZCFG.EXE)

I've experienced similar issues like that as well.  I started updating the XP clients last week with KB931836, which updates the workstation Daylight Savings Time start and end dates.  I’ve found in my testing that appointments that were already in exchange before the client was patched were one hour off, whereas appointments posted after the client patch are at the correct time.  Now when I run the tool the pre-patched appointments are right and the post-patch appointments are off.  

Also found that all day events that normally go from 12:00 to 12:00 can display from 11:00 to 11:00 making them look like multi-day events.  

Probably would have been best to patch everything all at once instead of over a few days.  What a mess. . .