problema gia affrontato per un sito, ho fatto cosi

<?
session_start();
if(!IsSet($sess))
{
$sess=session_id();
session_register("sess");
print " <script language=\"JavaScript\">";
print " var a=screen.width;";
print " var b=screen.height;";
print " var c=\"index.php?x=\"+a+\"&y=\"+b+\"&status=ok\";";
print " window.location=c;";
print " </script>";
die();
}

$x=$_GET['x'];
$y=$_GET['y'];
?>

queso script non invia a nessuna pagina ma solo a se stesso