This post on the PHPImpact blog talks about a compiler that helps to bridge some of the gap between PHP and .NET - Phlanger.

Phalanger is a new PHP implementation introducing the PHP language into the family of compiled .NET languages. [...] Phalanger compiles PHP scripts into MSIL (Microsoft Intermediate Language) which can be executed by .NET or Mono runtime.

He mentions some of the features of the tool (including interoperability between .NET and PHP and the ability to use current PHP libraries inside the .NET application). More information can be found on the Phlanger website.