You may use Goldwave Digital Audio editor. I use it regularly to extract audio from VOB files.
Rip the DVD and load the vob files into the audio editor.Select the audio portion you want to convert.You can directly convert the audio to MP3 if you have the lame encoder also installed.
The trial version of the audio editor has some limitations but I feel you can manage the job if it is just an one-time affair.( I have a fully licensed copy, though prior to purchasing I had used the trial version for many years. The limitations of the trial version could have changed over the years.So you have to try whether you can manage with the present limitations of the trial version)
You may also try the Mediacoder(Audio) which is freeware.The interface is a little daunting but still can be worked out.
http://mediacoder.sourceforge.net/audio/