Allow only certain websites to access a PHP page

Order allow, deny
Deny from 192.168.0.10
Deny from 212.155.
Deny from 1.2.3.4  5.6.7.8 127.0.0.1
Allow from all

Deny from all
Allow from 1.2.3.4

<?
    $allowed[0]="xxx.xxx.xxx.xxx";
    $allowed[1]="yyy.yyy.yyy.yyy";

    // add as many as you need

    if (!in_array($_SERVER['REMOTE_ADDR'],$allowed)) header("HTTP/1.1 403 Forbidden");
?>