Jquery PHP download displaying odd characters

[q1h]

I have a JQuery form:

      $("#download").live("submit", function () {
        $.ajax({
            type: "POST",
            cache: false,
            url: "download.php",
            data: $(this).serialize(),
            success: function (data) {
                $('#result').html(data);
            }
        });
        return false;
    });

Which submits to a PHP file:

PHP Code:

<?php
$file = $_POST['file'];
$url = '/uploads/' . $file . '.zip';
header("Cache-Control: public");
header("Content-Description: File Transfer");
header("Content-Disposition: attachment; filename=x.zip");
header("Content-Type: application/zip");
header("Content-Transfer-Encoding: binary");
readfile( $url );
exit();
?>

Which outputs garbled text into my "#result" div. I'm positive that the PHP is executing properly, but how can I get JQuery to prompt the download instead of reading as text? When I delete "$('#result').html(data);" nothing happens at all, and I can't just link to the PHP file because the form submits file-specific info. Thanks ...