This forum is closed. Thank you for your contributions.
A Wolfe,
If your customer has something to upgrade from, then an upgrade will work nicely.
Here are the supported upgrade paths: http://support.microsoft.com/kb/292607/en-us
Otherwise, the customer will have to buy XP Home or Pro full retail or if appropriate, systembuilder/OEM. Or, the customer can participate in the Genuine Windows Offer, if s/he qualifies: http://www.microsoft.com/genuine/downloads/FAQ.aspx?displaylang=en#Question6Label