Trouble installing the PHP PDO driver for MSSQL on Windows and Xampp

Hello,

I'm having trouble connecting with MSSQL on Xampp/Windows
(dev local server connecting to a distant DB (MSSQL 2005)).

The following Connection string work fine :

'odbc:DRIVER={SQL Server}; SERVER=' . SQLSRV_IP . ',' . SQLSRV_PORT . ';DATABASE=' . SQLSRV_DBNAME

so I don't think it have anything to do with DB rights or firewall but

'mssql:host=' . SQLSRV_IP . ';dbname=' . SQLSRV_DBNAME, SQLSRV_USER, SQLSRV_PWD

give me the following error message : 'could not find driver'.

I've search the web and stumble upon the following link by MS (which I hope is the latest version)

http://www.microsoft.com/downloads/en/details.aspx?FamilyID=80e44913-24b4-4113-8807-caae6cf2ca05

I've installed the 4 .dll in /php/ext/ and added the following line in PHP.ini
extension=php_pdo_sqlsrv_53_ts_vc6.dll
extension=php_sqlsrv_53_ts_vc6.dll
but it still don't work (loading any other .dll give me various errors on apache startup)

Could someone tell me what I'm doing wrong or give me step by step instruction ?
I'm fairly new working with anything else than MySQL or PostgreSQL.

Thank you and kind regards.