Nero Vision Question

Hi ,

I have a question about Nero Vision Express 3 , making a DVD !!!

When Making a DVD and putting on AVI files , the program obviously
converts the files to fit the DVD movie MPEG 2 format.
Now the problem is that when the DVD is finished (Image file, or actual burned DVD) there is no sound !!! However there is a Media Program within Nero Vision Express calles Show Time where the sound is heared.
How come my dvd compilations don’t have sound in any other media Player like Windows Media Player and or Regular DVD players???

Also please recommend a so called DVD player , that supports avi files!!!
Thank you