This is a two part process...
You'll need DVD Decryptor (freeware) and AutoGK (also freeware).
In DVD Decryptor you'll be ripping the DVD movie to an IFO file.
Once that is complete load AutoGK, select the IFO file you just created (it will automatically get the .vob's you just created) select a destination defualt an audio track (usually movies have more than one audio track) and file size and let it go. Depending on the movie it should take approximately 45 minutes to an hour to complete.
The other program you can use after DVD Decryptor is Any Video Converter (also freeware). Instead of selecting the ifo file, select all the .vob files and then right click on the files and select "merge" (make sure they are in the correct order).
This program is a lot faster than autoGK BUT if your DVD has multiple audio tracks, it may not get the right one during conversion.
I believe you can get everything at
www.filehippo.com
Hope this helps