That's the beauty of DVD... There's no strict "megs per minute" or "bitrate", it's all up to whoever encodes the movie. If you're looking at backing up just the main title, this is usually possible if the disc has some extras on it as well, you can strip the extras and any audio tracks you don't want in VobBlanker. Some movies will still be too big, though. The goal (as shown in VobBlanker) is to fit it within 4477MB.
As for AnyDVD, never used it, but I assume it will be clear when it's done. Software is usually clear about these sorts of things.