its been out for about a month, but say hello to the XNA Game Studio Express
it seems its free for windows, but there could be a fee involved for 360 (dont know yet, im at work and plan to research it fully when i get home, heh).
Originally Posted by XNA Website
XNA Game Studio Express 1.0 Released
The XNA team is proud to announce the availability of the 1.0 release of XNA Game Studio Express and the XNA Framework, aimed at helping students and hobbyists build games for Windows and the Xbox 360. This release supports both Windows game development and Xbox 360 development (subscription to the XNA Creators Club is required in order to run XNA-based games on the Xbox 360)
at the current time, running 360 games requires a hard drive, but it seems they hope to have CD/DVD and/or memory card based games in the future for ppl to share their games.