PHP + XML ครับช่วยหน่อยครับ ถ้าผมมี form การกรอกข้อมูล เมื่อ กด submit แล้วจะนำตัวแปรข้อมูลที่ได้มา

<?php
function writeXML($xml)
{
	$fp = fopen('xml5.xml', 'w+');
	fwrite($fp,$xml);
	fclose($fp);
}

if(isset($submit))
{
	$album = $_POST['album'];
	$track = $_POST['track'];
	$desc = $_POST['desc'];
	// Set the content type to be XML, so that the browser will   recognise it as XML.
	header( "content-type: application/xml; charset=utf-8" );

	// "Create" the document.
	$xml = new DOMDocument( "1.0", "utf-8" );

	// Create some elements.
	$xml_album = $xml->createElement( "Album" );

	// Create another element, just to show you can add any (realistic to computer) number of sublevels.
	$xml_name = $xml->createElement( "Name",$album );
	$xml_track = $xml->createElement( "Track", $track );
	$xml_note = $xml->createElement( "Description", $desc );

	// Append the whole bunch.
	$xml_album->appendChild( $xml_name );
	$xml_album->appendChild( $xml_note );
	$xml_album->appendChild( $xml_track );

	// Append the DOMXML.
	$xml->appendChild( $xml_album );

	// Parse the XML.
	$text = $xml->saveXML();
	print $text;

	writeXML($text);
}
else
{
?>
<form method="post" name="formxml" action="<?=$SERVER_['PHP_SELF'] ?>">
Album Name : <input type="text" name="album"></br>
Track Name : <input type="text" name="track"></br>
Track Description : <input type="text" name="desc"></br>
<input type="submit" name="submit" value="  Add  "></br>
</form>
<?
}
?>