Originally posted by Big Booger
With his CD key you will not be allowed to activate it, thus what is the point of installing it, that is if he has already activated his copy, AFAIK. BUt to answer your question:
Run regedit and go to: HKey_Local_MachineSoftwareMicrosoftWindowsNTCurrent VersionWPAEvents, on the right double click on "oobetimer" and it might be located there... I not 100% sure about it though.

It might also be located on the CD itself in the winnt.sif file located in the I386 folder... but I am not 100% sure about that either.

If anyone knows for sure I would be interested in this, if it is not illegal.
BB
B.B found an answer for you about find xp product key, and if it can be found in your sys files or cd contents

Windows XP converts the product key to the system's product ID. Exposing this product ID opens security concerns around the product ID generation process and the security of the product key. Therefore, that is why you should make sure you keep track of all product keys you use.