http://docs.php.net/manual/de/pdo.construct.php says:
PDO::__construct() ( string $dsn, ...
[...]
In general, a DSN consists of the PDO driver name, followed by a colon, followed by the PDO driver-specific connection syntax
try it with (edit: fixed Database= keyword)
new pdo( 'sqlsrv:Server=websvr\sqlwebdata,1433;Database=xxxx',
see also: http://php.net/ref.pdo-sqlsrv.connection