In 2007, Daylight Savings Time started on 11th March 2007, three weeks earlier than normal. Daylight Savings Time is ending this year one week later than usual, on 4th November (tomorrow). Because in 2007 we've had four more weeks of Daylight Savings Time, your PC's date and time may be affected when Daylight Savings Time ends this weekend.
If you are a Windows Vista user and have Automatic Updates configured for Windows Update, you most likely already have the necessary update to ensure your date and time will make the change come the 4th.
However, if you are unsure whether your Windows Vista PC has the update, you can go to the Daylight Savings Time Help and Support Center at Microsoft.com and use the associated wizard to get the necessary update for your PC. If your Windows Vista PC already has the update, when attempting to install the update you will be alerted that it does not apply to your system.
Another way to check to see if your Windows Vista PC has the correct update for this weekend's time change is to click on the clock in the lower right-hand corner of the taskbar. A pop-up will appear with the date and time and an alert about Daylight Savings Time ending on 4th November and that your PC will automatically fall back one hour at 2:00am on that date.
You can check here to see a list of all Microsoft products affected by Daylight Savings Time and the necessary updates needed for these products to properly accept the changes to Daylight Savings Time this year.DST, Daylight Saving Time, Microsoft
Source:→ Windows Vista Team blog