IF you want to Mix music & original sound you may need premier or another editing mpeg,*.avi,*.mpg,*.asf,*.mov,*.flv,*.wma,.. software ,you also can use the HIDEN because few people know that there is a editing movie software hiden inside win. Xp microsoft moviemaker is in c:/program files /movie maker/moviemk.exe....(Personaly I don't like it ) I rather adobe premier or my favorite video edit magic Both are payware softwares.
after you Capture the video using Fraps or the FSX recorder ,(because fsx have it own capture system) You will import this video to the open editing software to the TIMELINE video and sound wich should be shown separatly in two channels ,you must import to the extra audio channel the other sound could be a mp3 ,*.wav,*. wma etc format as a song, for example .
because all these software work diferent rfom each other I can not give you details of how to import or slice this chanel audio ,video, transitions ,effects, levels,etc
But you can follow the intructions of the windows movie maker..
