dis is what ya do. This method will save you a ton of space.

Go to your FS9 folder and look for the aircraft folder. If you know what the plane's folder name is, look for it. Open it up.....you'll have about 4 folders..., model, panel, sound and texture. Sometimes, they'll be multiple texture folders.....but anyways. Open the sound folder. If its the default sound, it'll be a simple config file. Open the file using notepad and make sure you save it so all config files can be opened via notepad. Close it out.....this will become useful later on in life. Take the downloaded sound and make sure its one complete folder with nothing more inside it but the sounds and a config file. Make sure its named "sound". Take that folder and drop it inside the still open aircraft folder. When somethin pops up say "Over write" or somethin along those lines, over write it. Exit outta all folders and BAM! You got a fresh 732 with real JT8d sounds. I recommend use'in the sounds from a DC-9 because you can hear the engines better.

Now...if you dont want to go thru all that, simply open the sound folder within the aircraft folder....leave it open. Open the custom sound folder all the way to where the sounds themselves are visible. Copy everything within that folder.....EVERYTHING!! revert back to your aircraft's sound folder. Paste the copied sounds within said sound folder. Overwrite whatever needs to be overwrite'in.....which normally will be the config file and WHAM!! You're there. Close out everything...delete the downloaded sounds and call it a day!

Next time, ill sling over a method that'll help you save a ton of space once you start download'in custom sounds.