The key factor is resolution. The real DVDs are at 720X576 or 720X480 pixels wide in 16:9 Widescreen format, for comversion use a bitrate of 2 MB atleast with Dr.DivX 2
In my case, i use the quality factor to rip movies, Insane quality mode, high noise reduction, quality preset of 10, bitrate of 2MBPS for Video, & 192kbps mp3 audio. The size comes out to be more then 700MB sometimes, but it's worth it. I catalog in DVD anyway as AVI files