I have a computer which died. It is for sure the motherboard ... replaced every part possible with no luck. So I purchased a new Motherboard (different manufacturer than current), cpu, ram, psu. The hard drive still appears to be fine so what I would like to do is try to boot up windows with the new mobo and see if it works. If not I will do a non-destructive reinstall of WinXP. If this doesn't work then I will just have to format/reinstall windows. I have 3 questions though.

1. Is there a file on the hard drive which will tell me which version of Windows XP the computer has? I know it is retail but not sure if its pro/home. There is no sticker on the comp.
2. The computer has SP3. I'm sure the retail version has either no SP or SP1 maybe. What happens if I do this non-destructive reinstall with a lesser SP than the one on the computer. I know I could slipstream it but I've had problems in the past with the product keys not working because they are generated based on the SP on the cd (I think).
3. If I remember correctly last time I did this I had a bit of trouble getting windows XP to activate ... but I think I only replaced the hard drive. Has anyone had experience in dealing with MS about this? Do they actually allow you to change mobo and reinstall? I guess to them this looks like a new computer ... but is it possible to get them to reactivate?

That is all!
Thanks so much!