http://support.microsoft.com/gp/cp_dst
Daylight Saving Time Help and Support Center
Beginning in 2007, daylight saving time (DST) will be extended in the United States. DST will start on March 11, 2007, which is three weeks earlier than usual, and it will end on November 4, 2007, which is one week later than usual. This results in a new DST period that is four weeks longer than in previous years. Unless certain updates are applied to your computer, the time zone settings for your computer's system clock may be incorrect during this four-week period. In particular, you must make sure that both your Windows operating system and your calendar programs are updated.