Andrew,
I did as you suggested and searched Microsoft's web site for
any articles that would back up your claim. Sorry to say, I
couldn't find any. Maybe you would be so kind as to supply
links to the articles you've found.
However, I did find a few articles that you might find
interesting. In the first article notice the YES entry in the
Windows XP Professional column next to the line for Windows XP
Home Edition.
Upgrading from Previous Versions of Windows
http://www.microsoft.com/windowsxp/pro/upgrading/matrix.mspx
In the next article there is only one scenario mentioned where
you cannot upgrade from Home to Pro: "Microsoft does not
support upgrading Windows XP Home Edition with Service Pack 1
(SP1) to Windows XP Professional without SP1." Translated, you
need to maintain the same service pack level when running the
upgrade.
Windows XP supported upgrade paths
http://support.microsoft.com/default.aspx?scid=kb;en-us;292607
You'd be doing us all a big favor if you could pass along the
source of your information. Obviously, you've got some inside
info that the rest of us can't seem to access.
Thanks
Nepatsfan