Connecting to MS SQL Server 2000 using PHP with Windows Credentials - php

Question

I know this is not a new question because i found lots of similar questions but not the one which solves my issue.
Well my question is how do i connect to a remote sql 2000 server using other domain windows credentials (not the one im logged in with) with php running on apache (xampp)... and the server doesnt run named instance.
These the things i tried,
installed SQL Native client for my php 5.3
got the .dll files to the ext folder
made sure i got the sqlsrv up and running via phpinfo
mssql.secureconnections is on
edited the php.ini and restart the apache server
So, i tried looking at various posts here and elsewhere but couldnt actually solve my problem.
i tried several codes, but here is the one which im currently trying with
$server = "XXX_Server";
$connInfo = array( "Database"=>"DB_Server", "UID"=>"username", "PWD"=>"password");
$conn = sqlsrv_connect($server, $connInfo);
if( $conn )
{
echo "Connection established.";
}
else
{
echo "Connection could not be established.";
die( print_r( sqlsrv_errors(), true));
}
and i get error as shown below,
Connection could not be established.
Array ( [0] => Array ( [0] => 28000 [SQLSTATE] => 28000 [1] => 18456 [code] => 18456 [2] => [Microsoft][SQL Server Native Client 10.0][SQL Server]Login failed for user 'xx\username'. [message] => [Microsoft][SQL Server Native Client 10.0][SQL Server]Login failed for user 'xx\username'. ) [1] => Array ( [0] => 28000 [SQLSTATE] => 28000 [1] => 18456 [code] => 18456 [2] => [Microsoft][SQL Server Native Client 10.0][SQL Server]Login failed for user 'xx\username'. [message] => [Microsoft][SQL Server Native Client 10.0][SQL Server]Login failed for user 'xx\username'. ) )
where xx = domain
And please note that , the client has given me a windows credentials which has access to the server and must use only this. And when i hardcoded my credentials (which has access too) in the script, it didnt work and got the error above, but when i use QueryExpress / SQL Studio, im able to access the db using windows credentials (mine).
So to make it simple, i need to write a script where i need to hardcode the windows credentials and connect to a SQL DB (Stuck here) and make the script accessible for only few using windows ad authentication (which i know how to do)
Please provide me some tips and advice as im stuck and dont know how to proceed. Whatever i research and try, i end up doing the same thing, facing a wall :P
Thanks in advance