Both are the same operating system, however Pro allows better security
controls of user accounts. If you have multiple users, and you need to lock
down your system from prying 5-year-olds, I'd use Pro. If you need Remote
Desktop or have to log on to a Domain, you'll need Pro.
Do your homework, study which options you need or want, and also take a look
at the upgrade version. It is less expensive for the full version, but
needs a qualifying previous operating system:
http://www.microsoft.com/windowsxp/home/howtobuy/upgrading/default.asp
