A complete re-install will be necessary as you are changing to a completely new chipset.
You can run the free version of this program to find your Windows Product Key, along with some others like Microsoft Office - http://www.magicaljellybean.com/keyfinder/
However, be warned that it my not activate depending on what type of licence you have. If it is an OEM licence (what you get when they come pre-installed) the chances are it won't activate. The licence is tied to your machine and with the new parts, it will no longer recognise it as the same machine.
If it is a Retail version, which is normally what you get when you buy Windows separately, then you should be ok.
You won't know for sure until you try! Sometimes the can be very lenient.