Hi Ed. If you haven't already seen it this tute might help.
http://www.simviation.com/fsxaircraftinstall.htmIf you've tried that & still have problems post again. Give an example of an aircraft you've tried & a link or page number of the page it's posted on. Then someone can check it out for you & walk you through it.
Please note: The default location for FSX in Vista is
C:\Program Files\Microsoft Games\Microsoft Flight Simulator X
UNLESS you have Vista 64-bit. In this case it will be
C:\Program Files (x86)\Microsoft Games\Microsoft Flight Simulator X