A friend plays a lot of Japanese games and uses Windows XP with Service Pack 1. Service Pack 2 is known to break a lot of game compatibilities. Microsoft said, on their site, that Service Pack 2 is *required* for the update to daylight saving time!
Also, she takes online classes that require correct time, and manually setting the clock won't cut it.
I poked around and found they have an update for Windows 2000: http://support.microsoft.com/gp/dst_hu2?systemlist=w32
Which lets you download a program to manually set your timezone stuff. So I suggested she try that instead of installing Service Pack 2, and it worked. Your mileage may vary.