Was XP already installed on that hard drive from another PC? If so, then that almost never works right, and you must reinstall XP on the new hard drive so it can properly detect your hardware.
Thanks for getting back to me. I think the lesson I need to take from this particularly irritating computer experience is "leave the work to those who know how to do it". My PC is now working, after an intervention by experts, and I've only lost self-respect and a quantity of data. So it goes.