According to this post on O'Reilly's ONLamp.com website, Microsoft has released a new five page PDF file titled "PHP on Windows: Community Involvement Improves Performance" discussing the relationship between the software giant and the language over recent years.

The first effort described is the partnership between Microsoft and Zend that resulted in the development of the FastCGI Extension that essentially allowed PHP to be a first-class citizen when used on a Windows Server with IIS. The second effort described is the Microsoft SQL Server 2005 Driver for PHP developed internally by the SQL Server team.

They also mention Phlanger and the PHP for Microsoft Ajax projects.