On the Developer Tutorials site, there's an article talking about the integration that can be made with PHP6 and .NET Visual Studio:

PHP, .net and Silverlight will be integrated out of the box, along with Visual Studio 2008. The project has long been in the works, but our sources have informed us of an impending announcement that PHP 6 will ship with .net.

The glue between them is a part of the phlanger project.