You can use Microsoft SQL server with PHP It purely depends on what your server setup is (i.e windows or linux) see this page for additional help:
http://uk.php.net/mssql
I'm trying to connect to a MS SQL Server Express 2005 using PDO for ODBC, but I need the DSN string. I tried with:
$dsn = 'odbc:DRIVER={SQL Server};HOSTNAME=CCTPV608SQLEXPRESS;DATABASE=db_ibripos';
but it doesn't work, please help.