[MEncoder-users] What is the perfect bitrate for 720 in width a screen?

[Stass]

If I rip DVD into AVI at the normal width-height ratio with width say 
720, what is the perfect bitrate for such a screen? I was told 1800 
isn't enough. Then what?

And another question: why I can't get at the same quality like DVD an 
AVI for the same at least file size like VOB was or even less? I do 
understan that while compressin some quality is lost, but is it so a 
great loss?!