You need a software DVD-video player, that's all it plays, doesn't play other media files, just DVD-videos.
The two most popular are 'WinDVD' and 'PowerDVD' and they are usually supplied with new DVD-ROM drives so you can play DVD-video 'straight out of the box' without further expense.
However, if you already have a drive but no player-software, you
will have to buy either WinDVD or PowerDVD yourself, from a software supplier. You can download trial-versions I think.
PowerDVD Here:
http://www.gocyberlink.com/english/p....jsp?ProdId=28
WinDVD Here:
http://www.intervideo.com/jsp/Home.jsp
Be aware that to get smooth video playback you need a CPU of at least Pentium 600Mhz, failing that you'll need to get a dedicated MPEG-decoder card to take the strain off the CPU.