Installing PHP on Windows
Download PHP. On the FAQ page click Installation and go to the Installation and Configuration page and from there to the Manual Installation page. They explain that you should unzip your download file into a directory, typically off your root: j:\php. Copy php.ini-production to php.ini and open it in an editor. There are a set of required directives that you need to configure. Just go through them patiently, one at a time. It is not so bad.
Next, go through the steps to get PHP working in IIS.