So I thought that I could just use my copy of Windows XP Pro from my laptop for my new computer.  I installed it no problem.  I even registered it.  So yesterday I reboot and it tells me that my hardware has changed significantly and that I had to re-register.  I go through the normal process and it tells me I can't.  I then call their support line and they tell me that because it was an OEM copy of Windows XP I couldn't transfer it to the new computer.  I would have to purchase a new copy.  Ugh.  Even worse I only had 3 days.  Today I went out to CompUSA and bought a new copy.  When I tried to register again with the new key it told me it was invalid.  I called up MS again told them the situation, they gave me a new key and it worked. 

The moral of the story?

Next time, just call up and say you bought a new copy.  They'll give you a key and you won't have to pay the $300 like I did.

Of course, at least I have a clean conscience knowing that I am legal.  Maybe it'll give me good karma or something.