What exactly is the XNA Framework?
The XNA Framework allows game developers to create modern games using the C# programming language and a rich set of development libraries. The XNA Framework provides its own content pipeline to make it easy to get rich content (3D, 2D, sound, etc.) from content creation sources into a game. The XNA Framework also provides a very high level of API unification across the Windows and 360 implementations, thus virtually eliminating the cost and effort required to port games between these two platforms.