It sounds like you need an MPEG2 codec. To verify that, get either MediaPlayerClassic or VideoLAN, neither need an MPEG2 codec:
http://www.videohelp.com/tools/sections/video-players
Okay, say your DVDs now play. Either continue using one of the above or get the codec. The trouble is, you'll have to either get it under license, or find a hacked one. Like this one, dunno how stable it is:
http://www.videohelp.com/tools/Stinkys_MPEG2_Codec
Or get the trial of PowerDVD, a payware player. Whether you buy it or not, it will install a good MPEG2 codec. Good luck.
