How to use Password() in PHP? Syntax problem?

Hello again.
I have tried to use password() in my login-script but it did not work.

My code is:

$sql = "SELECT * FROM users";
$sql .= " WHERE username ='" .
mysql_real_escape_string($_POST['username']) . "' ";
$sql .= " AND pwd = (PASSWORD( ' " . $_POST['pwd'] . " ' )) ";

What is wrong in this?
And how should I write it?

Thanks for all help!

Karl
.