Windows XP - Genuine Advantage replacement version?

Hi there,

I've recently been contacted by a customer whose computer was previously
"upgraded" by her nephew, as she has now purchased a legitimate copy of
Windows XP and would like my help making the "this copy of Windows has
been stolen by pirates" message go away.

The letter from Microsoft says to "insert this CD and install Windows in
the normal way" but it's my policy to always take a complete backup of
all the data on the drive before this and to allow for the time
reinstalling software & stuff I charge a fair bit for this. I thought it
might be cheaper for her if I just reactivated her machine using the new
CD key she has bought.

I've been doing computer support for a living for a couple of years and
frankly, it's not in my nature to run an install of Windows over a
previous install if I can possibly help it. I've managed to get away
with doing so so remarkably rarely that I consider still consider it
scary and dangerous - mostly either the system has been so h0sed up by
the kids' spyware that a format & install is a much better option, or I
am able to fix the problem in some other way.

So the lady has a hologrammed CD in her hand and a license number from
Microsoft and apart from the "embarrassing" (she's a little old lady)
orange message the system is in good shape. I tried changing the CD-key
by this method <http://tinyurl.com/55uby> but when I went to enter the
new key it wouldn't accept it, insisting that it's invalid. I tried
rebooting & the same thing. I think that if I cancel out of the change
product key screen the installation ID comes up blank, or all zeroes, or
something (then returns to an invalid key afterwards?) - in any case, I
couldn't enter is & the call centre in India couldn't give me a
confirmation ID for the installation IDs I was able to provide them with.

I'm assuming that the pirate copy on this lady's machine is the retail
or corporate version - I discovered this <http://tinyurl.com/ft9ws>
after I left the site, but didn't know about it at the time and don't
know if my tinkering will have broken that method. Is there any other
way to find out?

Is the problem that the version of Windows issued under Genuine
Advantage scheme OEM? Is there any way to find out?

Finally, am I just being paranoid about reinstalling on this machine?
Will doing a repair installation <http://tinyurl.com/6l9sm> be safe
enough, considering that the system is presently quite healthy? I am
assuming that this will be sufficient to match the Windows version to
the key and that activation will subsequently succeed.

Thanks in advance for all comments, I appreciate your time,

Stroller.