I recently uprgaded my Vista x64 PC to Windows 7 x64 Home Premium. I now want to upgrade to the professional version. I have all legal copies of both. When I upgrade to the pro version, can I then use the Win 7 Home Premium upgrade (with that FPP) on another device (laptop), since the pro upgrade will have it's own FPP?
technically you can but I imagine that legally you shouldn't. The upgrade is cheaper than the full version and Home is cheaper than premium so in reality you just paid a lot more for a 1 copy of a full version.
Despite this I am almost certain that you "Could" do as you wish if you were so inclined! :-)
If you were to purchase a full upgrade version of Windows 7 Pro AND NOT the Anytime Upgrade version of Win 7 Pro then yes, you could reuse that Windows 7 Home Premium upgrade.
If, however, you do an Anytime Upgrade, you are only legally allowed to upgrade that Home Premium to Professional, NOT the copy of Vista. This applies whether or not you have a different product key for Pro.
I had actually purchased the home premium upgrade for another machine, that died before the upgrade could be installed. I bought the pro version for my main PC but had trouble with the initial install because I was not running the pro version of Vista x64. So, now I am hoping that since I got the home premium up and running, that if I install the pro upgrade, it will work and I won't have to reinstall all my programs (as it wanted me to do originally).
In the meantime my laptop, that was running Windows 7 Home Premium had some kind of registry error and prevented the windows update from working and installing updates properly. It wouldn't let me install the SP1, either. Long story short, I tried to repair it with an upgradse version and my original FPP, and needles to say, it is majorly "F-ed" up. I have now resorted to using my recovery disc to reinstall the factory version of Windows, so this post is probably moot anyway. Since it was my laptop, I didn't keep many or major files on it and I backed up anything that I will need again. I just really didn't want to have to do the tweaks again.
I also was able to purchase both programs through discount programs, (and, they were HIGHLY discounted) so the money issue is not really a problem.