As you are no doubt aware, the U.S. Energy Policy Act of 2005 extended daylight saving time (DST) in the U.S. by four weeks. Starting in 2007, DST begins on the second Sunday in March instead of in April and ends the first Sunday in November. Canada adopted the same rules as the U.S.
While there are a number of sites that describe how to update your computer with the revised DST rules — I used the TZEdit.exe application on some older Windows boxes as described here — I found few that tell you how to check whether or not your computer is properly updated.
The line below indicates whether or not your computer is set up properly: