Don’t fret too much, this won’t take much time. I can assure you that..
Download this file ( windowsXPsp3 ). Once you have downloaded the file, login as administrator and run the file by double clicking it. Wait for the Confirmation Message on screen.
The Above file adds a few entries to the Windows Registry that makes Microsoft think that you are a part of the Private beta program.
Check for new updates on Windows Update. You should now see Windows XP SP3 listed in the available updates.
Download and install it. Reboot whenever necessary.
