Once XP is installed and activated, it'll only work on that machine. If you try to activate it on the new machine, the activation will fail.
If you can convince Microsoft of your situation they might give you a new Key.
I have an old Dell laptop that was really broken, so I used a Windows XP Professional OS disk from a different computer that crashed (and was thrown away) to reinstall windows. I would like to use this OS disk on another computer instead now - meaning that i dont want to use my old dell laptop anymore and would like to use my 2nd laptop. If I reinstall windows with that same disk on my second laptop, is all that is going to happen is that I wont be able to use my first laptop (dell)?
I hope I am explaining this well - you need more info just let me know!