You can try Mac DVD ripper (it's not free), it support convert DVD to AVI, MPEG, WMV, DivX, RM, MOV, 3GP, 3GP2, MP4, MP3, WAV, WMA, M4A, OGG, RA, etc for Mac os.
I also use Mactheripper with limited success. It depends on the quality of the actual dvd, too, scratches and what-not can wreak havoc on the rip. But the same probably goes for any ripper.