Tom, I use SUPER (for pc):
http://www.erightsoft.com/SUPER.html
You just have to grab-past your vob file from the dvd, give the details on the divx Format and it works quite fine and fast. Not the most efficient way of converting a dvd to an avi file, but a good compromise. And I use virtualdub (part of neodivx) to cut the files properly. With both softwares, i don't care too much about video quality but try to keep the audio quality as good as in the original dvd.