Mine

<?

$docID = '-1246174515665636969';

if ( ($xml = file_get_contents('http://video.google.com/videofeed?docid=' . $docID)) === false )
	die("could not fetch xml\n");

$doc = new DOMDocument();

if (! $doc->loadXML($xml))
	die("could not load xml\n");

$xpath = new DOMXPath($doc);
$xpath->registerNamespace('media', 'http://search.yahoo.com/mrss/');

$thumb = $xpath->query('/rss/channel/item/media:group/media:thumbnail/@url', $doc)->item(0)->nodeValue;
echo $thumb, "\n";

?>