At this time, access to development tools for the Xbox 360 video game console is limited to developers working on approved titles for licensed publishers. This will change over time, so check back for more information in the future.
If you want to learn more about how you can prepare for Xbox 360 development using a Windows PC, this document covers some of the basics."
The Word document linked above is not really new, it was already posted long time ago on our news, but the interesting part is Microsoft might plan to open development to more than just 'developers working on approved titles for licensed publishers' in the future. We'll have to wait to know how far Microsoft wants to go with this.
Thanks to Arti for news/link.