The chances are pretty close to certain that all of the hardware drivers you need are already installed. You may be lacking some application and perhaps the deCSS library to decrypt the movie.
If you haven't already configured your software sources (see the "Mandrake Control Center" Media Manager) to include the plf packages you need then the easiest way is to go to http://easyurpmi.zarb.org/
and follow the instructions there. It will probably be enough to add the plf free and non-free plus the contrib sources.
Once that is set up you should be able to fire up the Software Packages Installation wizard in the "Control Center" and pick your application software. The plf versions of Xine or Mplayer would be a good place to start. Kaffeine is also quite nice. If necessary (I cannot remember if it is automatically pulled in as a dependency) you can also select libdvdcss2-1.2.9-1.1.102plf. With that little lot on board the rest should be easy. Just putting a dvd in the drive should start Kaffeine and display your movie.
If not, note any errors you get and come back here.