Well, if it must be MSSQL, you can use ODBC or go with the native PHP functions for MSSQL. I don't know why that's not an option.
There is a little more work and a re-compile of PHP if it's installed on a Unix/Linux system, but it seems it would be a standard direct connection as opposed to ODBC.
http://www.php.net/manual/en/ref.mssql.php