ok, that's a little simpler:
<?php
if($_SERVER['REQUEST_METHOD'] == "POST") {
if((isset($_POST['element1']) && $_POST['element1'] == "yes") && (isset($_POST['element2']) && $_POST['element2'] == "yes") && (isset($_POST['element3']) && $_POST['element3'] == "yes") && (isset($_POST['element4']) && $_POST['element4'] == "yes")) {
header("Location: page1.php");
} else {
header("Location: page2.php");
}
}
?>
yes, the header code needs to come before any HTML on the page.