I add it in post production. I dont this the AVI files from the film viewer has audio, but you can use an audio capture program (ie:Goldwave) and set the input to the windows WAV output, record it there and then re-integrate it I suppose.
For dramatic effect, I use all new sounds (like they do in the movies
![Big Grin :D](http://bbs.hitechcreations.com/smf/Smileys/default/biggrin.gif)
) after I have all the clips together in a film.