Booting Up System Using HDD Saved From Dead System?

I have (or, rather, had) an eMachines desktop running XP Home. I fried its motherboard but the HDD remained intact. I pulled it out and found another system running XP Pro (a Dell Precision desktop). However, simply swapping the HDDs to boot up from the eMachines' drive on the Dell did not work: it complained about hardware mismatch and I could not even start Windows in Safe mode. Is there any way to do this? What else do I need to do to get it to work?I am trying to avoid getting a new computer at this point, so getting the Dell to "be just like" my old eMachines would be ideal.