Microsoft has quite a lot of literature geared towards getting people to move from PHP to its proprietary ASP.NET system. Unlike some of the Microsoft literature to its more hated enemies, such as Linux, the ASP.NET migration information is actually fairly well thought out and makes interesting reading.
If you are currently an ASP.NET developer and are considering PHP, give this document a read - it will help you fully understand the differences between PHP and ASP.NET. Having said that, remember it is written by Microsoft about a language they obviously want to promote - take the facts presented with a pinch of salt unless you can verify them elsewhere.
Due to the ever-shifting nature of MSDN articles, it is hard for me to provide a URL that will work for more than a month. Running a Google search for "php msdn" should turn it all up.