I am new to Linux, so I don't know much about Linux software... but I DO decrypt and convert DVD's for the purpose of putting them on my portable media player (Zune).
I use 2 programs (both Windows unfortunately, and I have no idea whether they will work in Wine or not.):
1. DVD Decrypter
or DVD Shrink
(My milage varies between the two. I think it depends on what the manufacturer does to encrypt the DVDs.)
The idea is that you use one of the backup tools (Decrypter or Shrink) to save the DVD image to your hard drive- unencrypted. (< - Key word here.) Then you use MediaCoder to convert the DVD video file (.vob) to a more portable, smaller file. (In my case, it's .mp4) The nice thing about Media Coder is that it will convert practically ANYTHING to practically ANYTHING. It's not the most user-friendly software, but it is POWERFUL. For my Zune, there is a drop down menu at the top that allows you to select a portable media player. (Note: Firefox must be installed for this to work) Different players have different options, and some may work better than others (I know my option for a .wmv container made my Zune software convert it back to .mp4 when I tried to sync- so it wasn't worth it.) so you will have to experiment, but it's pretty point and click.
Now, if you want to simply convert the audio, that should actually be easier and you wont even need the portable-media-player-interface. At the bottom of the software's window, it has tabs dictating the Video and Audio settings for the file you are trying to create. Somewhere (sorry, I would be posting screen shots and everything showing you how to do this if my fs wasn't corrupted by GParted a while back... and I am operating entirely on memory) there is an option like "Enable Video"- make sure that is unchecked. Next go to the options for audio and make sure "enable audio" IS checked. Set the format you want the audio to be encoded to, click start and let the software do it's magic. When it's done, you will have all of the .vob file converted to an audio file.
But wait: you want them to be mashed together into one big audio file. No problem. Before you click start, notice a dropdown menu that is just below the information 'tree' that is likely to be set to Default. Click that till and select Join, to join the files together during conversion. Then click start.
I hope this helps... if you actually read this and it doesn't make sense(likely), or you need more help, feel free to PM/Email me and I will help you the best I can.