Windows XP Expiration something to consider
I know, someone is going to say "What do you mean - my O.S. doesn't expire?". Well if you have an O.E.M. version of XP running on a machine and the machine dies then the liscense for the O.S. dies also. I have been informed by M$ that they will not issue an activation code to me because O.E.M. XP can not be "transferred" to another machine. If I were to buy a retail copy of XP then it could be transfered and they would issue another activation code.
So everyone who buys a new machine with XP on it and reconfigures the machine enough to require a new activation code, or who's machine dies and you try to get going on another machine - well - you're out of luck. You will need to head down to the nearest M$ outlet and get another copy of the O.S.