1) Double-click My Computer
2) Double-click on the "C" drive
3) Go to the C:\Windows\System32 folder (you may have to click on the link that says "Show The contents of this folder")
4) Find the files "wpa.dbl" and "wpa.bak" and copy them to a safe location. You can copy them on a floppy drive or burn it onto a CD or DVD.
5) After you have reinstalled Windows XP on your reformatted hard drive, click "No" when asked if you want to go ahead and go through the activation process
6) Reboot your computer into SafeMode (you can either press F8 as Windows is booting up to see the Windows Advanced Options menu and select SAFEBOOT_OPTION=Minimal or follow the instructions in Starting Windows XP in SafeMode
7) Double-click My Computer
8) Double-click on the "C" drive
9) Go to the C:\Windows\System32 folder (you may have to click on the link that says "Show The contents of this folder")
10) Find the file "wpa.dbl" and "wpa.bak" (if it exists) and rename them to "wpadbl.new" and "wpabak.new"
11) Copy your original "wpa.dbl" and "wpa.bak" files from your floppy disk, CD or DVD into the C:\Windows\System32 folder
12) Restart your system (if you followed the directions in Starting Windows XP in SafeMode you may need to go back into MSCONFIG to turn off booting into SafeMode).

This only works on the same machine that previously had windows XP on it. If you are changing the motherboard then you would need reactivation anyway. So using your old WPA files would have needed reactivation anyways! This works on machines that have no internet connection and is handy for a machine built in the shop and later taken out to a worksite with no intenet, and the user has corrupted windows to the point of needing a reload of the operating system! Using this method you won't have to take it back to the shop for reactivation!