fastsky,
Aerofly pro deluxe add on disc can be a bit difficualt to install. My friend had the same problem.
Uninstall it, use add/remove programes in control panel, then restart the PC, and try again.
Hopefully this will help.
BTW, you can download extra planes for free from www.rc-sim.de
I have loads now, I can't even remember the ones that came with the sim or add on pack.
Great sim for planes, the harrier is great fun.
Just for fun, in any scenery except the photo realistic ones, you can select cockpit view and fly from the inside, again the harrier is fun here. And check out the back end of the carrier, thats all I'm saying