1) php_mssql extension : If you’d like something that has the same API mysql and mysqli has, then use the php_mssql extension. But there is a catch, the bundled ntwdblib.dll file with PHP is not working. You have to find this file from a SQL Server 2000 installation or you can find it on the Internet. This API is supposedly not very reliable but I have been using it without problem for about one year.
2) Microsoft SQL Server 2005 PHP Driver : If you’d like something more modern but which does not have the same API and is missing some important functions (mssql_num_rows). The big plus is that it is supported by Microsoft and is likely to work with a future version.