DirectX is a high-level API to access low-level graphics functions. Most modern video cards have drivers that support DirectX, making it easier to write applications with heavy graphics.
[>] DirectX for Visual Basic
An excellent site for DirectX information. The author goes to great lengths to satisfy all levels of experience in his audience, as he guides the user through the entire world of DirectX. The only downside is the lack of a search function -- there is so much code, and so many tutorials, finding the one document that deals with a specific problem can be tough.