Windows XP requires an update to be installed to deal with the new dates of Daylight Savings Time. Most likely your computer has already downloaded and installed this update; however in the unlikely chance that your PC hasn’t, we are providing the link to the Microsoft Download site for this update. It is important that you be running Windows XP Service Pack 2 (XPSP2) in order to install this update.
The site is:
Microsoft Windows Update
Mac OS X
There is a similar update available for OS X.
Any computer configured to use a time server (NTP) will automatically adjust its clock based on the remote server time. No software update is necessary in this case.
Please check this out for answers to many questions concerning the shift in Daylight Savings Time and your computer.