What exactly is a "clean install?

[Lynn]

Basic question here.
Is a "clean install" on Windows XP one where I have to
reformat the hard disk and then install Windows. A "clean
install" is not an install that you do "on top" of an
existing version of Windows, right? Can anyone clarify
these terms.
My problem is I have a neighbor who has a version of
Windows XP that cannot be updated. He gets the message
from the Windows Update sight saying that the Product Key
is invalid. There is a knowledge base article that
describes this but it says to perform a "clean install"
with the original Windows CD. Can I just install Windows
on top of itself? Or do I have to start from scratch.
Lynn

 

[Kevin]

yeah, do it from scratch. I dont see there is another way.

 

[Lynn]

Crusty -
Do I have to install Windows XP on a clean formatted disk
or can I install it on top of itself to add the product
key change.