yeah you get like 10 activations with each windows install OS disk >>>> once you exceed that you need to call microsoft to get a new activation number; but given your situtation and having built a new computer I will be shocked if they accomodate you with a manufactured computer builder disk; MS is going to send you back to the original builder that supplied you with the disk; I think you can figure out how that conversation is going to go ?
You need to buy a retail version of Win XP I saw them cheap on ebay and genuine ones too
http://cgi.ebay.com/Microsoft-Window...QQcmdZViewItem