Did you read the insructions in you order confirmation email?
Challenge response can usually be done from another PC that is connected to the net, you just write down the challenge code from your music pc take it to you other net connected pc and register with the challenge code on their website, it will give you a response code you then take that back to your non net connected pc and enter it, - done
Did win XP compatibility mode not work?
id email nomad for some support if it didnt