I enjoyed this article about Vista.
http://www.linux-watch.com/news/NS2930812631.html

Although I don't predict that MS will open source Vista. I think they have one more chance at a Windows OS, possibly in 2009, then they'll have to release their own version of Linux.

I read recently that Bill Gates was set to retire in 2008. I can easily see him pulling a Steve Jobs, coming back in a few years, and revamping the company with Microsoft Linux and Office Linux.

Microsoft won't be able to compete any other way:

1. Wine keeps getting better. Eventually, it will be able to run all Windows apps flawlessly.
2. Improvements to Winelib and Mono will allow Windows developers to easily port their existing apps to Linux.
3. Free virtualization software from VMWare currently allows you to convert and run your existing Windows partition in Linux. The hardware requirements of virtualization are less than what Vista needs. Virtualization gives you the best of both worlds, a modern, stable, and secure OS (thanks to Linux), and compatibility with your must-have Windows XP software (thanks to the VMWare virtual machine).

Here's a link to an article about how to convert your existing Windows partition to a VMWare virtual machine:
http://www.howtoforge.com/vmware_converter_windows_linux

It really is that easy.  So even if MS does open source Vista in the future, why bother?