I bought the upgrade version of XP. Fortunately I qualified. Primarily, I did it so that I could run Stardock products better.
Here is an interesting sidebar:
At my local computer shop I can purchase WinXP(Pro)full version for $500.00 (CDN) However, for $600.00 (CDN) I can get a new computer that is twice the computer I have now,
with XP installed. Sure, it's an OEM version, but considering the price advantage, if I were to do it all over again I'd go this route.