We currently offer a massive range of downloads for FSX, as well as older flight simulator add-ons for the ever-popular FS2004, FS2002, CFS3 and now becoming ever popular with dediced virtual aviators is Laminar Research's X-Plane series.
Set up a flight in FS with the plane you want parked at the airport you want to start from. Cut the engine, switch everything off, and save the flight (the ";" key). When you give the saved flight a name, there's a tick box to make this the default flight. Another trick is that you can start up FSX in any flight situation you like. Go to your "My Documents" folder, and open the "Flight Simulator X Files" subfolder. Locate a flight file (*.FLT) and right-click on it and choose "Open with", then click "Browse" to locate your fsx.exe file and click OK. Once you've done that, you can boot FSX directly into a given flight by double-clicking that FLT file.
RE: how to change the startup airplane and airport?