If I'm understanding the question correctly, then one of the simplest ways to convert is to demux the streams using your ripper program. Womble will let you then re-assemble the desired audio and video stream into a mpeg file without re-encoding.

DVD-Lab Pro has a wonderful demuxing tool. Drag the first VOB file in the sequence into the assets window and it'll split all of the remaining vobs into single, elementary streams. i.e. you'll get your video stream and each of your audio streams. Then use Womble to re-assemble the streams you want.

Don't forget that subtitles will be lost when you do this (assuming they aren't "burned in").