You can use Handbrake, which is a free program for this purpose. It can rip DVDs in pretty much any format.
Edit: You will need to install VLC for Handbrake to work with most DVDs. You can get that from http://www.videolan.org/vlc/download-windows.html .
After that, simply open up Handbrake and select the DVD as the source. It should have a number of preset export formats that will make it easy for you to convert the DVD to a relevant format.