Welcome to SimV! Hmm...
This may not help but:
Shut down FSX and delete the files you put in there
Go back to the zipped file, extract (unzip) to a temporary file
copy and paste the correct file to C:\Program Files\Microsoft Games\Microsoft Flight Simulator X\SimObjects\Airplanes
Start up FSX. (Make sure you check the "Show all variations" checkbox at the bottom of the Select Aircraft screen.
If your aircraft does not show up do the basics: Check if it is actually for another version of Flight Sim.
Check to see if it is an aircraft TEXTURE and not a modle.
If it is a TEXTURE ONLY and you do the steps it tells you to you may not have the correct modle (as it may be payware)
Hope this helped
