Acronis 10: a simple question (I hope)

My Gateway Media Center desktop crashed yesterday. Completely dead. I bought a used HP from a local tech shop. Nice little desktop, with one glaring problem: an 80 gig hard drive. This is a problem because the hard drive in the Gateway has a 250 gig hd, with about 115 gig of programs and data.

I very much want to continue using the Gateway hard drive. Both drives have Win XP Pro 3. The problem is, the old drive has a Gateway OEM version of XP. When I try to boot it, it gets as far as the Welcome screen, then the Microsoft screen pops up, saying I have to reactivate XP . I called the number on the screen. MS's computer asked for a 54 digit number, which I entered. It came back and declined to re-activate XP. No reason given.

Be aware I have a full (Acronis) backup on an external hd. Worst case, I was going to use Recovery Console to reinstall XP, then restore the backup. Problem with that is, Recovery would probably reinstall the same oem version of XP. It has also been suggested that Acronis would copy the same XP version onto the hard drive from the backup. I'm not real sure about that. Does Acronis copy the operating system files when it does a Drive C backup?

Appreciate any suggestions.

tbone