Use DVD Decryptor to rip the dvd onto your computer. Use IFO mode and only rip the main movie. You will be able to tell which file to get by the length of the file (same time as the movie). The default is almost always the file you want.
Use AutoGK to encode the file to AVI. Select the IFO, that you just ripped, as the input. It will allow you to select audio tracks (the first one is almost always the correct one). You can also choose file size. Don't mess with anything else, there is no need. Add the job and click start.