yes Nero's conversion is very poor (to put it politely, it SUCKS!!). Many people are happy enough with them though lol.
Not sure what method you used? You can try this (I think CM mentioned this before):
on the latest versions of dvd2avi, instead of having audio to demux all tracks (that is the default), set it to just "Demux (AC3, MPA, DTS)" . Included a picture of this for you (choose the one highlighted in blue & see if this works better for you *should only give one file for sound).