RE: Real Flight 6.5 upgrade and 5.5 aircraft
Yes you CAN install the Expansion pack disks after RF 6.5 is installed.
What is the "trick"?
1 - Run the setup on the Expansion Pack Disks "as administrator" ( something you should also do on your Realflight installation ).
2 - The Expansion pack setup will need to be given the explicit path to the Realflight installation.
3 - Run Realflight as Administrator and you will prompted for the serial numbers the first time.
More info here: [link=http://www.knifeedge.com/forums/showthread.php?t=27806&highlight=expansion+pack]Info - Click me![/link]
But wait! There is an easier way!
If you have G5.5 you can use this MUCH EASIER method... ( note I wrote it for G3/G4 but it applies for G6.x )
[link=http://www.knifeedge.com/forums/showthread.php?t=24396&highlight=expansion+pack]Quick installation/transfer - Click me![/link]