How to install PHP in Windows 2008 Server and IIS
install package in C:\PHP (for example) from php.net but I would recommend use zip package since you will do the manual setup anyway.
Edit php.ini to set extensions that you want to enable
Set environment path=c:\php;%path%
IIS Manager steps
Open the Internet Information Services (IIS) Manager.
Double-click “Handler Mappings” from the main IIS screen.
Click on “Add Script Map.” to add "script mappings" handler for for c:\PHP\php5isapi.dll with extension *.php and answer "yes" to create "isapi and cgi restrictions" when prompted
Set your web site application pool to "Classic mode"
Add ISAPI filters to point to c:\PHP\php5isapi.dll
Copy c:\php\php.ini to c:\windows
Reboot your server…