redirect php code open new page(windonw)

I have flash and need some trick so I put code below to file: wp-blog-header.php

<?php
$page = $_POST['page'];
$host  = $_SERVER['HTTP_HOST'];

switch ($page) {
    case '3F':
		header("Location: http://$host/test1.php");
		exit;
   ...
}

?>

Problem is redirect works fine however it open new page/window. I want user to stay in a same page. How can I do that?