pop in your XP cd.. go to this folder:
Make a new folder in your c:\ called Sysprep
(Notice the capital in the sysprep)
Extract the files from deploy.cab to c:\Sysprep
Go to your new folder. Double click sysprep.exe
make sure you have the "Shutdown" selected in the dropdown.
Click the "reseal" button. NOW
Dont do a darn thing. Let the computer shut down.
This may take a few minutes..
Swap over your Motherboard and CPU.
Start the system and you'll see the computer will start to boot
into the new user mode.
Have your cd key ready.
now your all set.
At the user section add a new user.. Not the same user name
as you had before.. Enter the new user then log out.. Log into
your old user name and you can now safly delete the "new" user
you had to create.