you will need to run the PHP installer first, the configure your website in IIS admin to map .php files to the php.exe file. if thats in D:\PHP\ do this:
right click your website in Internet Services Manager.
click properties, in Home Directory tab, under appliacetion click configuration...
if .php is not in the list, click add..
-->in the executable box browse to your php.exe
-->in extension, type .php
-->click all verbs on
-->click script engine and check that file exists ON
click ok all the way out
if you want to store your PHP files in a differnt directory than that of your html files, you will need to set up a virtual directory i guess...