You cannot convert .msdvd files to any other multimedia files because these files are projects and do not contain the actual multimedia data, just references to it. However, you can use Windows Movie Maker and select the "publish to this computer" function and then choose the output file extension as AVI. Once you have AVI, you can use any of the available avi to mp3 conversion solutions to export the audio track.
Open MSDVD file Open MP3 file