I shipped the first public release of my own product today to coincide with ASP.NET AJAX 1.0. My project is called PHP for Microsoft AJAX Library, a small library to help PHP applications make use of the Microsoft AJAX Library. This is a shared source project under the Microsoft Permissive License, and I'd love your contributions!
The general idea behind the library is to create an easy to use link between PHP applications and the ASP.NET AJAX functionality. He gives an illustration of a simple web service (a "Hello World" type) with both the PHP script and the corresponding HTML to interface with it.