On the Server-Side Essentials blog for SitePoint.com today Akash Mehta has a new tutorial walking you through the beginning steps of using SQL Server Express and PHP with the help of the Windows Platform Installer.
This article assumes you have a basic understanding of PHP and relational databases - if you can write PHP and SQL code to manipulate database records, you're good to go. We'll move through the PHP fairly quickly, in order to focus on the power and simplicity of the platform.
You'll need to download the Web Platform Installer to follow along with the tutorial (or, obviously, have all of the needed software installed already). He walks you through the installation complete with screenshots including how to create the handler to let your PHP connect to the SQL Server backend and making some sample tables for PHP to select data from.