with xp you can't just take the drive out and stick it in another box.

well, sometimes you can if the motherboard chipsets are the same.

here are two links that pretty much describe the same method of moving a drive to a new mobo even if the chipsets are different..it should work for you. I would follow the instructions to the letter. I've known folks who've just moved the drive and weren't able to recover even after putting the drive back in the original box.. they had to reload xp..

http://www.michaelstevenstech.com/moving_xpfrm.html

http://www.theeldergeek.com/replace_motherboard.htm

edit : I should add that you'll probably want to back up your WPA file so that you won't need to activate again.. read this page.