As many of you know MS is requiring you to UPGRADE a qualifying OS (Win7 or Win8.1) in order to activate Windows 10..
And for those that would rather CLEAN install Windows 10 to another partition, drive or vhd - Win10 OS will not activate unless it is installed over a prior qualifying OS..
Well, until now that is, here is what is needed to CLEAN install Win10 and have it see a prior qualifying OS
Within the Win10 setup media is a file "\sources\gatherosstate.exe"
Copy "gatherosstate.exe" to the desktop of your qualifying OS
RightClick "gatherosstate.exe" and run as admin
"gatherosstate.exe" creates a "GenuineTicket.xml" file
Now you can Clean Install Win10 to disk or partition
or Apply the Win10 install.wim to VHD
NOTE: With Windows 10 as an Upgrade, Do not enter any product key when asked, just skip over the request..
Once Win10 is installed or applied
Copy "GenuineTicket.xml" into "\ProgramData\Microsoft\Windows\ClipSVC\GenuineTicket"
so you end up with "\ProgramData\Microsoft\Windows\ClipSVC\GenuineTicket\GenuineTicket.xml"
You just Clean installed Win10 and Upgraded your Qualifying OS without actually upgrading the prior OS
In my case > Created 50GB VHD > Applied Win10 to VHD > Copied "GenuineTicket.xml" = Activated Win10 VHDSource