I'm Win XP Home and installing aircraft is dead easy mate-
1- download the file (in this case a Boeing 777) to Desktop
2- Unzip it-
3- The unzipped yellow folder will now appear somewhere on desktop-
4- Click it to examine its contents, note the name of the plane is in its own subfolder-
5- Click the subfolder and you'll see the essential six things every aircraft in FSX must have, namely Model/Panel/Sound/Texture/aircraft file/cfg file.
(Some have more than that (optional liveries etc) but they're the 6 you must have)
6- Go back and Copy the plane subfolder-
7- and Paste it into the FSX 'Airplanes' folder-
8- and bingo! it should appear in the list of aircraft..