Here is the response to your question that had been posted in the thread. The thread had become split off a number of times and was moved to a work area for cleanup :
To install the pre-GF4 addons that KnifeEdge rewrote to work with G4:
For each file downloaded:
Locate the file on your disk.
Unzip the file. If you have Windows XP or Vista, you can just double-click it.
Extract the .zip file's contents to "C:\Program Files\RealFlightG4\Data" (assuming you installed G4 in the default location).
Now run RealFlight G4 or G4.5 and the Add-Ons content will be available in the aircraft and airport selection dialogs.
It doesn't matter where you download the zip folder/file.
"Locate the file on your disk." seems to be no problem. It appears you know where it is. It also appears that your double-click of the file is some trouble for you. So just un-zip it normally. And point the un-zip to the location that is mentioned. How to do that? That's normal Windows. Right click on the downloaded file (wherever it is) and follow the pop-up windows. You'll need to select where you want the extracted file to go, and that would be the location mentioned in the instructions above.