I have set up php on IIS 6.x a number of times. In that context, I have to change IIS itself to run as x86, and I can manually add php as a cgi extension.
The app I am using supports php 5.3 as the highet php version. So I can't use the nice new x64 supporting php versions, and the IIS native php support.
Where can I find docs/steps to set this up?
Answer is: Use the Microsoft Web Platform Installer, v5 or higher. It is quick and easy. I have never used Web Platform Installer before, but it is EASY. Two clicks and PHP is installed and running in IIS (2 or more versions available), MySQL (5.1 currently in the tool), and dozens of open sources apps (CMS systems, etc) both php/mysql and .net based.
If you have not tried Web Platform Installer, give it a throw. I am amazed I missed it until now. It downloads, installs and configures the tools you choose. It is by far the easiest way to install stuff on a windows server. It is, actually, easier and faster than the same on linux.