ibleedspeed said:
if you want an easy route use "womble mpeg2 video wizard" you just put your stereo audio into womble and go to the export tab then audio tab and choose 5.1 ac3. it may not be as good of a method as the tutorial i mentioned twice now. good luck bro.
That will sound TERRIBLE, it will have a terrible echo sound to it, if you want a really nice sounding 5.1 upmix you need to follow the guide that Doctor M did up.