First you need to enable IIS in windows vista, through enable windows features in control panel. make sure to enable ISAPI and CGI as they are required for PHP fastcgi mode,
also to to be able to use mssql server with PHP under IIS you need to have SQLServerDriverForPHP11 installed, after downloading and installing this file, you will have a few dll files, which you need to copy them into php/ext folder and enable this in php.ini file.
extension=php_sqlsrv_52_nts_vc6.dll