You could just rip it with Decryptor or Shrink (or even just copy the vobs over to your HD straight from the disc folders). Then, I use a program called Gold Wave to rip the audio tracks. From there I would make sure that the audio tracks link up to the picture from the other release. If it doesn't, you could tweak it in Vegas or something. Then I would use DVD Architect or whatever program you use in order to author the disc with multiple tracks.

But I am somewhat of a noob to this stuff, so others might have better suggestions.