When you activate Windows XP, Microsoft stores the data in the Windows Product Activation database files wpa.dbl and Wpa.bak in the folder %systemroot%\system32. If you change the motherboard or make significant hardware changes, XP will require you to reactive. But if you plan to reinstall XP on the same hardware, you can back up the activation status and then restore it after you reinstall and avoid the activation process. You can backup the Windows Product Activation database files to diskette. They are very small. A directory listing from my XP Pro workstation:
C:\WINDOWS\system32>dir wp*
Volume in drive C has no label.
Volume Serial Number is 8447-0571
Directory of C:\WINDOWS\system32
10/24/2001 08:28 PM 12,584 wpa.bak
01/14/2002 09:05 AM 12,642 wpa.dbl
After you reinstall XP, to restore the Windows Product Activation database files:
Start XP to Minimal Safe mode
Change directory to the \%systemroot%\system32 folder
Rename the newly created wpa.dbl to wpa.nonactivated and wpa.bak, if it exists, to wpabak.nonactivated.
Copy your backed up wpa.dbl and wpb.bak files to the system32 folder
Reboot
This should work if you want to avoid activating XP after a reinstall or restore on the same or very similar hardware. It will not work if the hardware is significantly different from that in place when the Windows Product Activation database files were created. This is not a hack to avoid activating installations.