Happen to need both ASP.NET and PHP running on the same IIS server? Josh Holmes (and Mark Brown) have you covered with this new presentation posted to Josh's blog.
I got a question the other day about running both ASP.NET and PHP on the same server and whether or not it works. The short answer I gave is "Yes". The longer answer, I'm going to give here. In point of fact, both ASP.NET and PHP work really well on the instance of IIS. They can't share session state but otherwise it's a very peaceful existence.
The slides from the presentation are included in the post. There's also a full tutorial on how to get things set up correctly so that PHP and ASP.NET can play nicely on the same machine.