Help getting XP reinstalled

I have received 3 computers from a co. that went out of business. All the HDs have been wiped, and XP was installed to the point of asking for the registration key. No matter what key was used (the one for that particular machine or others) none would work.

I used Boot & Nuke to start over from scratch, and now the media isn’t recognized and I cannot get XP to install. One of these machines is going to a daughter entering college soon, so I would like to figure out what is going on.

Any suggestions would be appreciated. Ive never run into something like this before.