1. decrypt DVD to hard drive
2. open files with dvd shrink
3. click the "analysis" button to perform a deep analysis (takes awhile but better quality, always use it when compressing heavily or where there's lots of black in the movie, or basically whenever you have the time)
4. click re-author button
5. in DVD browser (right side window) drag only the "main movie" to the left window
6. go to "compression settings" tab on right window:
- select only AC3 5.1-ch english (or whatever single audio you'd prefer, i prefer this for good quality and compatibility, without insane filesize. if youy want AC3 5.1 and DTS, get a dual layer DVD - or just buy the original?)
- can uncheck subpicture, but its usually like 2mb so...
- on the left hand side window, there's an icon which looks like two arrows pointing different directions, click it to set the start and end frames: the credits can actually take up quite a chunk of the filesize
If you want to keep the menu's and extras etc, backup the full disk but navigate through each item and for anything you're not interested in much, either manually set compression level low or replace with a still image. You can actually shrink away unwanted stuff to very low filesize but still keep menu functionality. Alternately there's other apps for making menu's but never tried - never felt the need.
For really heavy compression have a look for DivX or XviD, though DVDplayer compatibility goes out of the window.