Although not strictly necessary due to the speed of today's computers, a year or two ago a DVD decoder card was a necessity to anyone who wished to watch DVDs on his computer. It is still quite helpful today simply due to relieving some load on the CPU and letting the movie be piped out to a television set so more screen real-estate is free for surfing and normal use.

Good Windows DVD decoder cards are the Sigma Designs Hollywood Plus and the Creative Labs DXR3.