Latest: Microsoft PHP drivers for SQL Servers

Microsoft Drivers 3.2, 3.1, 3.0, and 2.0 for PHP for SQL Server provide connectivity to Microsoft SQL Server from PHP applications.

If you are interested in yet older versions of PHP review these posts:
http://hodentekmsss.blogspot.com/2014/11/php-driver-for-sql-server-released.html

http://hodentekmsss.blogspot.com/2010/05/phpbb-brings-interoperability-with-sql.html

You may install PHP from XAMPP here:
http://www.windows8downloads.com/win8-xampp.html

Recently 3/7/2015 Microsoft released Php drivers for SQL Servers. This single download consists of a number of drivers. Details area as shown:

These drivers are PHP 5 extensions that allow you to connect to SQL Server from PHP applications/scripts.

The SQLSRV3X extension provides a procedural interface while the PDO_SQLSRV extension implements PDO for accessing data in all editions of SQL Server 2005 and later (versions 3.2 and 3.1 require SQL Server 2008 and later).

The following OS are supported:
Windows 7, Windows 8, Windows 8.1, Windows Server 2008 R2, Windows Server 2008 Service Pack 2, Windows Vista Service Pack 2

Of course you need PHP 5x to make use of these drivers.

Driver / PHP versions support:

Version 3.2 supports PHP 5.6, 5.5, and 5.4

Version 3.1 supports PHP 5.5 and 5.4

Version 3.0 supports PHP 5.4.

When you run the executable (SQLSRV32.exe for example) you will be asked to point to the path of the extension. You may have multiple version related paths as shown here on Windows 8.1 here:

C:\Program Files (x86)\PHP\v5.6  
C:\Program Files (x86)\PHP\v5.3

Download the driver to mathc your PHP version here:
http://www.microsoft.com/en-us/download/details.aspx?id=20098&WT.mc_id=Blog_SQL_Announce_DI