I know how to load .ISO file on DVDShrink. This is not the problem. After the file is loaded, the video is all messed up and DVDShrink is unable to compress it.
It's a ashame that you are unable to improve DVDDecripter because I really like it. My only concern is not it is unable to decode certain newer release movies.
IMGBurn would be perfect for me only if it has the ability to compress files to fit 4.7GB disc because the double layer discs are still somewhat pricey. :-(