CookieRevised gives good advice. Remove / disconnect non-essential hardware, such as modems, sound cards, printers and so forth. If you can get XP installed that way, you might even get lucky and not have any problems after putting it all back together. Some hardware combinations don't respond well to all the probing during detection.
You mentioned upgrading your motherboard and CPU -- what are they? Do you know the watt rating of your power supply? That's a common problem with upgrades reusing old cases. I wouldn't necessarily rule it out, even though Windows 2000 installed ok.
There is a
rather nasty procedure for diagnosing and working around driver conflict issues during Windows setup, but hopefully you won't need that.
