How to add subtitle to a dvd and to a divx/xvid !

I have a movie.It´s a divx i think,cuz only the divx player was able to play it.I want to know how to add to it a subtitle.And i would like to know how to do that to a DVD too.
And what program do i need to convert .txt to a .sub or many other


P.S,I would also need a video and audio identifier cuz i have shark tale and it sais that the audio format is invalid so id like to know what format it is.