Ironic that DoD ( F o r u m _ I d i o t ) is saying that only idiots would want an MS server isn't it...?
Anyway, you need to keep an open mind and look at the benefits and drawbacks of each.
ASP .NET ( and all the rest of the .NET framework for that matter ) definitally has PHP stomped when you're dealing with OOP code. .NET has a pretty complete implementation of OOP concepts, AND has shared classes that are common to the entire .NET framework. Definitally a plus if you're developing in more than one language. Because of the ILM compilation .NET deals with, theres also the benefit of being able to actually program in more than one language and use the objects / methods / whatever from each language in another language pretty seamlessly. Have one guy program in C++ with .NET, interface with ASP .NET seamlessly.
ASP .NET also supports more than just one language, whereas with PHP... you have only PHP. With ASP .NET, you have access to ASP, C#, C++, JScript, etc. etc.
I would say PHP's connectivity, especially to databases, is FAR superior to ASPs. In .NET, everything is ADO.NET, which adds overhead. Not to mention the lack of well-supported and free databases on Windows platform.
Also, we should consider costs. PHP is free, as are Linux/UNIX OS's that it usually runs on. MySQL is free too, as is PostgreSQL. With MS, you're gonna have to pay for the OS, Webserver, database ( if you're using MSSQL ). Course, depending on who you have on staff, support could be potentially a lot cheaper. But it depends on the situation.
You have to consider your app too. DoD gives the example of a forum... but remember that for most companies, a pre-built forum is not what they're after. Many companies have custom-built applications, so it wont really matter so much what you can download for free.
I personally like PHP, its fast to program in, fast executing, and fun to goof around with. BUT remember to keep yoru options open and examine the language for what you need in it, not for what everyone else thinks you need. Who knows, maybe Perl or ColdFusion are a better choice for you!