Unfortunately, I have the exact same problem, so my post does not offer any solutions. But for those out there who are more skilled and for those who perhaps doubt that there is something strange going on here, I would like to outline all the steps I took:
1) When I got my phone (recently), there was an added sheet advising that DST updates may need to be done, so I went to the web-site and followed all 4 steps. The first was to make sure all Windows XP updates are complete. Since it is my work computer that I synch with, and IT has recently changed policies to force and enforce all updates, I have no choice in the matter. All updates have been done, as our IT department is very quick to act on all updates. We are also running Windows XP SP2, which should cover all updates of this nature inherently.
2) The second step said to make sure the Microsoft Outlook updates have been run. Since we have Office 2003 at work, I followed the steps and eventually led to running a file labelled TMZMOVE.EXE. I was elated, because a few appointments needed to be updated, so I thought I was on the right track. I checked appointments all the way through until December, covering the next time change as well.
3) I checked my version of Active Sync, and according to the steps, I needed to upgrade to Active Sync version 4.5. There was a little pain involved there, because I had already done my first sync with the old version of Active Sync installed, so the installer already noticed another profile, and wouldn't let me modify any settings from the previous. I had to create a new profile that synch'ed with nothing, go back and change to old profile, do some juggling, do the hokey-pokey, and voila, 30 minutes later, I was able to synch again.
4) Install the Windows Mobile DST Update tool.
The end result, it didn't seem to work. I have some appointments that are on, and some that are off by an hour. I began to operate under the assumption that maybe some of my old appointments were the cause of the problem then I got a new meeting invite. I accepted. The appointment was correct in Outlook, and 1 hour off on my new Treo. Yay! I'll be early for all meetings!
Any ideas are welcome at this point. I am in Canada, and more specifically BC. But we do observe DST here, and should be in the same time zone as California.