I know what the original poster is talking about when it comes to the upgrade path. I have trouble loading RF as well till I got down path what it takes to do it (in my case anyway). I always have to do the following for a complete reload :

Note: This is for XP Professional only as that what I have.

1) Install my original RealFlight Deluxe CD (AND DON'T RUN THE PROGRAM !)
2) Install RealFlight G2 (I think I had to follow a KB article on the RealFlight web site to get it to install although it may not be necessary now)
3) Go register the my copy again
4) Download the latest updates
5) Install my add-on CD's (1,2,3)
6) Adjust the graphics settings as needed

I have learned through time to install G2 on another drive besides C:. That way, if I reload Windows or the software, I do not loose my planes, settings, etc., etc.. Course, you could back them up as well if you are running on C: and restore if needed.

HTH,

CJ