I posted an annoucement on the Media Center Sandbox site earlier today, and I want to cross-post it here to make sure that everyone sees it. I'm really excited to announce that the final beta 2 version of the Windows Media Center SDK (build 5384.4) for Windows Vista beta 2 has been released on the Microsoft Connect site. We will also be releasing it to the MSDN Subscriber site in the next couple of days.
If you're interested in developing applications for Windows Media Center, this build of the SDK is a great chance to get started. As always, make sure to let us know any feedback you have by reporting bugs on the Connect site and posting comments/questions on the Media Center development forum.