php no mssql. Couldn't connect sqlsrv_connect with PHP 5.4.5

Good morning,

I have installed Windows 2008 Server with IIS 7.5 and PHP Version 5.4.5. This compiled with VC9. On this server I have also installed Sharepoint connecting to SQL Server 2008 on another server.

I have to connect to a database on another server, which is in SQL Server 2000.

In the code I had connected with mssql in php, but I think it is no longer in use and replaced by sqlsrv.

I downloaded the dll and I put in php.ini. The extension_dir path I have it right.

For the connection does not work, the browser tells me:
"PHP Fatal error: Call to undefined function sqlsrv_connect () in ...."

What can be happening?

thanks