Video and sound don't coincide in my converted movies?

I have many "rm" extension movie files. I'm trying to convert them to 3gp in orders to watch them on my 6303 nokia mobile. I tried converting using "Joboshare 3GP video converter, however when i play the converted movie either on my PC or on my mobile the picture and the sound don't coincide. Do I have to use other application or there is something I have to edit in the configuration of the convert process????