The SQL Server team just announced the release of their latest PHP driver for SQL Server. Details about the release can be found at http://blogs.msdn.com/b/sqlphp/archive/2010/08/04/microsoft-drivers-for-php-for-sql-server-2-0-released.aspx.
A major highlight of this release has been the introduction of PDO drivers for SQL Server. This means the PHP application developer now need not care about database but rather focus on the application code.
Source : The Official Microsoft IIS Site