HI.. I'm a long time user of FSnavigator, you should have no problems. Its a while (since I got FS2004) since I've installed it but from memory just run the setup file. Make sure you answer the question about which version of MSFS you have.. After installation, run the FSnavDBC program - this will link the program into FS. After a restart, run FS and when it has loaded, press F9 - the key then toggles between the FS and FSnavigator screens. Great program, easy to use.
It will work irrespective of aircraft, although the program is fairly limited in the aircraft it officially supports - so, if you have a medium range twin jet which doesnt appear on the FSnavigator list, select something similar like an F-100. Your fuel, speed, cruise calculations should work out about right.
You'll see what I mean when you try it!
Tim