I honestly don't know. I just built my computer from scratch, and went ahead and spent the $200 on the XP Pro upgrade, just to avoid any possible problems.
As far as unregistered software, I was told that the way XP Home, and XP Pro send and receive info when doing updates is different. Something about XP Pro doesn't send unnecessary info, whereas Home does, and that is how they detect unregistered software.
Maybe someone else can jump in and clarify what I'm tring to say, or prove me wrong.