Why does it have to be to AVI? You could rip the DVD to VOB format using DVD Decrypter, then use SUPER to convert directly from VOB to DPG I believe.

EDIT: But if you are set on converting to AVI, you can use AutoGK to convert from VOB to AVI. From my experiences, SUPER isn't fantastic. So it may be better to do it this way. I have used AutoGK for converting videos for my DS before, and it worked out quite well (although that was for my Max Media Player, not MoonShell). There's a tutorial here: http://www.autogk.me.uk/modules.php?name=TutorialEN

Use DVD Decrypter to rip the VOB files. Google for tutorials on it.

 

You could try checking out dpg4x. It's a pretty nifty converter that I actually think is a decent recommendation and has some extra things that DPGTools doesn't have.

 

I don't recall SUPER being slow or complicated, but I do know it's UI being buggy as all hell.

 

use super you have to convert the file into something smaller like mpeg4 before you can convert it to .dpg using super.