For non Blu-Ray DVD's you need the DeCSS decrption library -- usually obtainable in Linux Distros as LIBDVDCSS.
An easy way to get this for Windows is to install a trial version of say WINDVD. Don't activate it. Now install VLC -- some versions of VLC won't have the DeCSS library in it so it will pick up the DeCSS library from WINDVD.
Play a DVD with VLC and whilst playing uninstall WINDVD -- it won't remove the DeCSS library while its being used in another application.
Now you should have FREE DVD playing. And tell all those smarmy DRM supporting Lawyers to "Go and Make a sexual Move with a Duck"