For running the software, you may need to deal with installing in compatibility mode, but it is not hard. A call to Horizon should give you info as to whether you can register/activate it or not.
If they have not hurt legacy versions with their licensing changes, consider strongly getting a used copy of RF 8 - ask about that too. Starting with that one, you can use any device Windows sees as a joystick/game pad, and don't need their dedicated box. Some transmitters allow for a USB connection to the PC just for that purpose. Spektrum and Frsky also sell dongles to plug into USB that allow you to use their transmitters normally/wirelessly. Going that route requires more fiddling to get the channels/functions mapped to the in game functions, but once done gives a cheaper alternative to buying the full thing with their dedicated box.