The easiest way to install PHP on Windows is to use Microsoft's Web Platform Installer.
To install PHP with the Web Platform Installer, select the Products tab at the top of the window and select the following packages (by pressing the Add buttons next to the packages):
- PHP 5.4.x
- Microsoft Drivers 3.0 for PHP 5.4 for SQL Server in IIS
The SQL Driver package is required by TestRail to connect to SQL Server databases. It's recommended to install the package even if you plan to use TestRail with a MySQL database. Now install both packages and all dependencies (such as IIS itself) by clicking the Install button. Please make sure to install the full IIS Edition and not IIS Express.
If you don't want to use the Web Platform Installer to install PHP, Microsoft also explains how to install PHP manually on IIS 6 and IIS 7. Also, if you plan to use a SQL Server database (instead of MySQL), also install the Microsoft SQL Server Driver for PHP when installing PHP manually. The driver needs the SQL Server Native Client to be installed (this is installed automatically for you when you use the Web Platform Installer).