I remember hearing on the Max PC podcast, someone mentioned something about calling up Microsoft technical support and pleading your case to them. Apparently if you spin it a certain way (or maybe it was blatantly lying... "I'm not sure what happened, this is the motherboard I've always used, I was just restoring the OS and the disc won't take!") and make enough noise, they'll fix it for you.
I just don't remember the exact details of how this was done.
Microsoft has been proven in years past to show some compassion (I know scary right) when it comes to the product keys and licenses for the older OSs (XP, Vista, and even 7) being used more than once. You typically have to be the same owner and it usually has to be an extreme case such as motherboard replacement, HDD failure and motherboard replacement, etc. You can spin it however you want but if the HAL.dll file that gets sent to Microsoft when you connect to the internet for the first time reports back to them that there has been a board change and you are trying to use the same license, they will reject it. That's also why you see several people telling others to call them, not try it over the web because they can override the authentication process and give you an approval code to make it genuine.