Microsoft DirectX is a collection of application programming interfaces (APIs) for handling tasks related to multimedia, especially game programming and video, on Microsoft platforms. Originally, the names of these APIs all began with Direct, such as Direct3D, DirectDraw, DirectMusic, DirectPlay, DirectSound, and so forth. DirectX, then, was the generic term for all of these APIs and became the name of the collection.
Windows 7 is expected to support full software rendering of DirectX 10 and 10.1 features.
Vista required you to have a DirectX 10 graphics accelerator to be able to display certain features. So Windows 7 desktop is expected to be available with complete features for everyone, regardless of what graphics card their system has.