Thats basically all the key points, well done klm
For those who want it in a bit more detail:
Other sites to download free aircraft are:
Theres 1000s of aircraft, textures, scenery etc files on each of these sites.
When you download an aircraft, it will usually download as a .zip file. If you havent done so already, I suggest you use Winzip, found at http://www.winzip.com/downwz.htm
(its a trial version, but after the, I think its 30 days, you just click 'remind me later' every time you open it...I've never registered, naughty me.
Once you have Winzip installed (Windows XP does have its own utility built in, but its not as good) when you double click one of your downloads, it will open up a Winzip window. This should now show you all of the files found inside the .zip file. Scroll down to see if there is a readme, if there is, look at it (double-click on it); this will often help in installing the aircraft correctly. If there is a setup.exe file in there, great. Double click on it, and follow the installation instructions, which you must be able to do, seeing as you managed to installed flight simulator in the first place.
However, very few developers (as many do it for free) can be bothered to create a self-installing (.exe) file, so you have to do it yourself a majority of the time. The safe way to do it is to click 'extract' and extract the whole thing (all the files-make sure 'all files' is selected) to a temporary location, such as in 'My Documents' or a directory of your choosing (make sure 'use folder names' is selected in the 'extract...' window). Then, go to that location, and have a look at the folder that has been created. Say you downloaded a Boeing 767. It may be titled '7672' or something. Open the folder, and take a look inside. You may find lots of folders, saying 'model' 'texture' 'panel' 'sound' and often some others too, along with files such as aircraft.cfg. This whole folder is the main aircraft folder. You must drag and drop the entire folder (click 'back' and move the folder containing the previously mentioned items) into the FS9\Aircraft folder. As KLM said, this is usually 'C:\Program Files\Microsoft Games\Flight Simulator 9\Aircraft' but for some people it may be different (i.e., for me, it is 'F:\Program Files\Microsoft Games\Flight Simulator 2004\Aircraft'). Check what yours is.
If that was the only folder inside the original extracted folder, then you're done. But many aircraft come with other files, such as guages and effects files. In your main extracted folder (which contained the folder which contained the 'model' 'panel' 'texture' folders (getting confusing now, huh? Its not that bad once you know how, which doesnt take long)) you may find other folders which contain .gau and .fx files. Simply drag the contents of these into the 'C:\Program Files\Microsoft Games\Flight Simulator 9\Effects' and 'C:\Program Files\Microsoft Games\Flight Simulator 9\Gauges' folders. But you're not dragging the entire containing folder this time--just the contents.
Thats the basics of installing aircraft. Theres also the issue of installing repaints for aircraft you already have and installing scenery.
I hope this helps too