You will find your answer here:
http://doom9.org/mpg/subs_and_multiple_audio_tracks.htm
Note: I-Author is a commercial program, the demo of which is not available. You can find the program by doing searches (
www.hotbot.com, www.google.com, www.alltheweb.com).
Note2: I-Author can only be bought in Asia. If you have the demo version and would like to apply a "crack" it is my understanding you cannot request for such a crack *here*.
Good luck!!