You don't change the CD - you use sysprep and an answer file to insert the
key (ref.chm from the support\tools\deploy.cab on your XP CD) in the
unattend.txt file under UserData... It would look similar to this:
ProductKey = "XXXXX-XXXXX-XXXXX-XXXXX-XXXXX" (obviously X won't cut it.)
"We approached the case, you remember, with an absolutely blank mind,
which is always an advantage. We had formed no theories. We were simply
there to observe and to draw inferences from our observations." -
Sherlock Holmes