At the game developer conference GDC 2006, they handed out DVDs with this dev kit for the Xbox 360, but you can download too – “The XNA Framework is an exciting new development and execution environment which will allow game developers to more easily create games which run on the Microsoft Windows and Xbox 360 platforms. Microsoft XNA Build is a tool and set of technologies which will help game studios manage the growing complexities of their game content builds. The first pre-release of XNA Build is now available for download. We invite you to install this pre-release into a non-production environment to learn more about how XNA Build will reduce development complexities.” [via] – Link.

Related: XNA Overview – Link.