Depends on how your editing your films. If your using a video editing program, most will let you add audio tracks.
I used After Effects to edit my shots and Audition to edit my audio. It was kinda involved doing it this way but I think it's the best way.
Anyway, in your video editing program place the gun sounds in the timeline. I used custom sounds mixed with the game sounds., but the game sounds are fine.
If by chance you have an audio editing program, edit all your video and then import it into your audio editing program and place the sounds sync'ed with the video. Some audio programs have effects you can use to enhance your audio files. Audition has one called "Doppler" that I was able to add the doppler fx to the game sounds as the planes flew by.
Hope this helps,
~kc
My Film:
http://www.fotgfilms.com/newProjectPages/kc.html
