Sure, Vista Media Center's only been officially available for a few months. But onwards and upwards. Microsoft is already prepping the next version of Windows Media Center, which may or may not be codenamed Fiji. And the company is looking for beta testers. Over the last few years, Microsoft has had a track record of releasing new versions of Windows Media Center every year or two. While Windows Vista includes Media Center functionality, the company is expected to release the next version of Media Center before the next full Windows release. Fiji could be available in 2007 or 2008, while the next major operating system upgrade is slated for 2009.
In order to apply as for a beta account, you'll have to fill out a series of questions and basically prove that you've got the right stuff to test out a new system and provide constructive feedback. Those selected as testers will be notified by May 31st.
MythTV, the popular Linux based PVR project, has been around for some time. It's nice, and it functions well, but it's only as functional as Windows Media Center Edition plus, it can be difficult to install and configure. 
