K-Lite Codec Pack Corporate is a useful colelction of video, audio and graphic codecs designed especially for use in a corporate environment.Media Player Classic Home Cinema 1.1.843 - This is a full-featured player which has internal decoding support for DVD, MPEG-2, MP2, MP3, AAC, AC3 and DTS. It also has internal support for opening MP4, Matroska and Ogg containers. Media Player Classic is also capable of playing QuickTime and RealMedia content if those codecs are installed.
DScaler5 also support playback of DVD video in Windows Media Player and Windows Media Center. Windows Vista (Home Premium / Ultimate) already contains its own MPEG-2 and DVD decoder. So you don't need to install one of these, unless you prefer them over the MS decoder.