You can use DVD Decrypter for this. Get it
here. When you use it make sure you are in IFO mode from the mode menu and in the Tools menus goto settings. In settings go to the IFO Mode tab and make sure the File Splitting drop down is set to None.
Then from the main screen on the right it should have already selected the correct VTS and PGC for you. You should see a list of chapters down below that. Just uncheck the chapters that you don't want. Don't mess with the Cells just the Chapters.
Then just click on the button with a picture of a DVD to the HDD. That will give you a single VOB file with your Chapter on it. Then to convert the VOB file to AVI just use Super found
here. That is a completely free way to do it and no need for trial software. If you have trouble just ask back here.