$now = time();

($sec,$min,$hour,$mday,$mon,$year,$wday,$rest) = localtime($now);
if ($wday !=4) {
    $dow = $wday;
    if ($dow < 4) {
      $dow += 7;
    }
    $then = (($dow - 4) * 60 * 60 * 24);
}

($sec,$min,$hour,$mday,$mon,$year,$rest) = localtime($now - $then);
$mon=$mon+1;
$year=$year+1900;