"Play games that require DirectX 8.1 for Win2000"
DirectX is a set of libraries containing the technology and information needed for your computer to launch applications that base their content on graphics, music and video. In other words, your graphics and sound cards, apart from their corresponding drivers, need DirectX to know how to respond to each program.
Normally, you already have DirectX installed on your computer, but you often have to check that the version is correct, otherwise you won't be able to enjoy the latest news in 2D video playback or 2D games or 3D animations, as DirectX is updated according to the needs of the new programs.