@istizan; Şu örnek sana yardımcı olacaktır.

<?php
	
	header("Content-Type: text/xml; charset=UTF-8");
	
	echo "<"."?"."xml version=\"1.0\" encoding=\"UTF-8\""."?".">";
	
	/**
	* Verileri direk diziden alıyorum. Sen verileri
	* veritabanında çekip eklersin. Mantığı öğrenmen
	* açısından bunu veriyorum.
	*/
	function get_results()
	{
		return array(
			(object) array(
				"type" => "video",
				"thumb" => "media/videos/thumbs/html5.png",
				"source" => array(
					"http://www.youtube.com/watch?v=siOHh0uzcuY"
				),
				"description" => "Youtube Video: Introduction to HTML5"
			),
			(object) array(
				"type" => "audio",
				"thumb" => "media/audio/thumbs/audio1.jpg",
				"source" => array(
					"media/audio/audio1.ogg",
					"media/audio/audio1.mp3"
				),
				"description" => "Audio Example"
			),
			(object) array(
				"type" => "video",
				"thumb" => "media/videos/thumbs/video1.png",
				"source" => array(
					"http://www.youtube.com/watch?v=irF02LNZLpE"
				),
				"description" => "Youtube Video: San Francisco Carnaval Grand Parade 2010"
			),
			(object) array(
				"type" => "video",
				"thumb" => "media/videos/thumbs/video2.png",
				"source" => array(
					"http://www.youtube.com/watch?v=dD1H4fvdnyI"
				),
				"description" => "Youtube Video: San Francisco Carnival Parade 2010 Best Video"
			)
		);
	}
	
	$results = get_results();
	
	echo "<MultimediaGallery>";
	
	foreach($results as $result)
	{
		echo "<file type=\"" . $result->type . "\">";
		
		echo "<thumb>{$result->thumb}</thumb>";
		
		foreach($result->source as $source)
		{
			echo "<source>{$source}</source>";
		}
		
		echo "<description>{$result->description}</description>";
		
		echo "</file>";
	}
	
	echo "</MultimediaGallery>";