You can synchronize your computer time automatically with internet standard time server. Normally this feature is enabled by default in Windows XP and Windows Vista. If not then you can enable it now.
For Windows XP, double click on the computer clock at the bottom right corner and go to “Internet Time” tab. Under “Date and Time Properties” windows, tick the check box labeled “Automatically synchronize with an internet time server”, and you can select the alternative time server using drop down list.
For Windows Vista, left click the computer clock at the bottom right and click the blue link “Change date and time settings…”.
Under “Internet Time” tab, click on the “Change settings…” button and then tick the check box labeled “Synchronize with an internet time server”.
Now, your computer will periodically update time with internet time server but you can force your computer also for immediate synchronization. For manual synchronizing click the “Update Now” button.