[PHP\MSSQL]Unable to connect

I set a web-server on a dedicated machine and I installed SQL Server 2005 64 bit, I made a php connection using mssql_connect() but unluckily I failed to connect. I already tried many times changing ntwdblib.dll but it failed also. I'm also sure that the SERVERNAME\INSTANCE,USER,PASS is correct. What should I do? I already tried going to http://www.php.net/function.mssql-connect and read the posts below but it didn't helped. I'm using Windows Server 2003 Enterprise Edition Service Pack 2 64 bit, I'm using xampp as web-server, I'm using SQL Server 2005 64bit, and I'm using ntwdblib.dl version=200.80.194.0.