Need to format your hard drive and reinstall XP, and don’t want to have to go through the product activation process again? You can save the activation status info and then restore it after you reinstall the operating system, as long as you haven’t made any changes to the hardware. Here’s how:
Before reformatting, in My Computer, double click the drive letter on which you installed XP, and navigate to WINDOWS\System32.
Click “Show the contents of this folder” if necessary.
Copy the following files to a external HDD, USB drive, CD/DVD or network location: wpa.dbl and wpa.bak.
After reformatting and reinstalling XP, select NO when asked if you want to activate Windows now.
Restart in Safe Mode.
In My Computer, open the WINDOWS\System32 folder and rename the existing wpa.dbl and wpa.bak files (if you have them).
Now copy your old wpa.dbl and wpa.bak files to the System32 folder.
Restart and you should not be requested to activate again. This only works when you reinstall Windows on the same computer and the hardware remains the same.