"NVIDIA DVD Decoder enables the industry's highest quality DVD and MPEG-2 playback and rich surround sound audio for Windows Media Player and Windows Media Center Edition. Featuring Dolby® Digital surround sound audio and hardware acceleration for compatible graphics processors, the NVIDIA DVD Decoder delivers unmatched color fidelity and smooth DVD, video, and TV viewing. When paired with a GeForce GPU, NVIDIA DVD Decoder enables adaptive de-interlacing and high quality filtering for the ultimate home theater experience."
If you have an nVidia-based GPU on your computer, and you use that computer to watch DVDs or MPEG2 files, this is a superb solution (I bought it myself yesterday).