Office XP technical questions

I have 2 questions regarding the office XP license:

1. Is there a way to find out which license was used to activate the suite? We have 4 or 5 different licenses, but we forgot which was used on which computers.

2. How does the license work? What part of the computer does the Microsoft activation check when looking to see if the license was already installed on a previous computer? If I do a clean install from windows 2000 to windows XP, will I be able to use the same license?

Keith