If I'm not mistaken, this is the official Microsoft guide to changing
the Win XP CD key.
Click on Start and then Run.
In the text box in the Run window, type regedit and click OK. This will
open the Registry Editor program.
Locate the HKEY_LOCAL_MACHINE folder under My Computer and click on the
(+) sign next the folder name to expand the folder.
Continue to expand folders until you reach the
HKEY_LOCAL_MACHINE\Software\Microsoft\WindowsNT\Current Version\WPAEvents
registry key.
Click on the WPAEvents folder.
In the results that appear in the window on the right, locate OOBETimer.
Right-click on the OOBETimer entry and choose Modify from the resulting
menu.
Change at least one digit in the Value data text box and click OK. This
will deactivate Windows XP.
Click on Start and then Run.
In the text box in the Run window, type the following command and click
OK.
%systemroot%\system32\oobe\msoobe.exe /a
When the Windows Product Activation window appears, choose Yes, I want
to telephone a customer service representative to activate Windows and
then click Next.
Click Change Product Key.
Type your new, valid Windows XP product key in the New key text boxes
and then click Update.
If you're taken back to the previous screen and prompted, choose Remind
me later.
