The Open Source at Microsoft site is a really good location for information, resources, and links on open source activities. I found the Spikesource tidbit very beneficial -
Spikesource is proud to offer the first open source PHP applications tested and validated for Windows Server 2008. Learn more...
On October 16, 2007, OSI approved two Microsoft Shared Source licenses—the Microsoft Public License (Ms-Pl) and the Microsoft Reciprocal License (Ms-Rl). Jon Rosenberg has more on Port 25 regarding these licenses, the approval process, and the continued excitement of Microsoft about participating in the open source community.
Cross Posted from Dan Fay's Blog (http://blogs.msdn.com/dan_fay)