On SitePoint.com today there's a quick tutorial showing how you can quickly and easily install PHP on Windows via the Web Platform Installer.

Earlier this year Microsoft released a small piece of software called the Web Platform Installer (Web PI)—a dead-simple way to install a complete suite of web software on your Windows machine. [...] To show you how simple it is to use and to give you an idea of what software is available, I’ll walk through the installation of PHP with the Web PI, as well as a few key PHP apps from scratch.

Once you have it downloaded and configured, you can go over to the "Web Platform" tab and select PHP to be installed (still in the PHP 5.2 series). Under the web applications tab there's various apps you can also install including WordPress and SugarCRM. Click "Install" and you should be all set - the Installer sets up the webserver (IIS) running PHP and a database (like MySQL or SQL Server).