By default MS Windows treats the CMOS clock as local time. This is irritating if you run multiple operating systems as both try and correct for DST shifts, it also seems (to me) to be a less elegant way of handling the problem.
I recently discovered a registry hack which allows you to tell it to treat the CMOS clock as UTC - just 1 key is needed. A .reg file is available here which you can download and use. Thanks to Eivind Eklund for the information (originally buried in here).
I have tested it on a Windows XP Pro system, but I expect it works on XP Home, Server 2003, NT and 2000.