Yes. XP is very hardware particular and won't socialize when massive hardware changes take place, such as what you propose. That's by design so that you must buy an operating system for each hardware setup.
I'm not sure, you could try to look up some stuff on Google if you like.
But as far as I know, Windows needs drivers for all the hardware, etc. Like he said, it's hardware specific so I can't imagine you being able to boot it off an external drive to whatever computer you like.
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