Hagar,
Also when it tells you this file could harm your PC take heed!

this particular file will NOT harm your computer in any way, shape, or form!!!! This file is perfectly safe, as it pertains to ONLY Flight Simulator. It is a scenery file that only works with flight simulator (in this case FS2004). fsx, has its own fsx/scenery/world file, as i assume, FS2000 and FS2002 do also.
Being that MICROSOFT made the game; and it is TESTED by Micro$oft, your WINDOWS VISTA was made by MICROSOFT...... are you seeing a trend???? Microsoft would not make something to damage something else of theirs!