Noted at http://en.wikipedia.org/wiki/VLC_media_player it plays DVDs.
Too bad you didn't tell about your make PC. Some like HP have a special install step to fetch the extra software.
I recently formatted my hard drive and I lost the software needed to watch DVD's on my pc. Where can I download new free software? My dvd drive is a Lite-On. Is the software the same for all makers of optical drives? Thanks