How to install legal Windows XP using serial number?

I am about to format the hard drive of a friend's machine and reinstall everything from scratch including his Operating System.

He has Windows XP Home Edition on it which is what I intend to reinstate.

The problem is that he doesn't have the Windows XP CD and the machine doesn't have a hidden recovery partition or anything like that.

There is a certificate of authenticity on the side of the machine with the Operating System's serial number.
Magic Jelly Bean Keyfinder suggests that the Operating System is actually activated using a different serial number.

I have copies of lots of Operating Systems here. What is my best option for making a legal (and activated) reinstall of his Operating System?

Many thanks for any help.

Reinstall using your disk and the serial number on the case. If there is an issue when activating, then call MS and explain the situation (except about Magic Jelly Bean and the disparate keys) and they will give you an activation key..

Phone up the MS activation telephone number and make sure the serial number stuck on the machine is valid. If so use that one.

Thanks for your replies guys.
Do I want to be installing OEM or Retail version?

In reply to a post by VWGolfman:

Thanks for your replies guys.
Do I want to be installing OEM or Retail version?

Same thing, OEM (after SP 1) requires a SLIC 1.0 in the bios, (which a legit machine will have already), OEM licence files (which can be installed on your disc or after you install the OS) & an OEM key (magic jellybeen is showing that key) the COA should pick up on the bios SLIC & allow you to activate by phone, any more info, google MDL forum.

Edit: all OEM files need to be the same make as your mainbord.

Edited by deleted (Sat 14-Nov-09 20:16:05)

Thank you David.
I guess the BIOS has SLIC 1.0 but I don't know which files should be on the CD in order to SLP activate.

I'll use the serial on the side of the machine and phone MS then. I hear they no longer have online activation. Is that correct?

Online activation is still there - I used it just the other day..