I believe that you will not need a key to upgrade, but you must upgrade your existing installation first, which will then create and then send to MS a hardware ID. After this is done, then you can go ahead and do a clean install and at the part where it asks for a key to be provided, just skip this step and the installation will proceed and will activate via the hardware ID created during the initial upgrade. No more keys required, it will all be done via a hardware ID.