So, if the DVD does not have a whole bunch of security and copy right protection features on it. You can just download the Microsoft Windows Live Movie Maker, open it up and click the button to add videos and drag the dvd disc over. And then go to save as and selected the WP7 options (there is a high quality and low quality).
If it has some protection on it, you have a little more work to do and I am not sure if we are allowed to say on here, since it is technically illegal violating those copy right protection things.