Eğer sadece "imgoriginalname" bu veriyi çekecekseniz aşağıdaki gibi kullanabilirsiniz.
Performans açısından

<?php  
header('Content-Type: text/xml');  
echo "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n";  
include("baglan.php");  
$sorgu=mysql_query("SELECT imgoriginalname FROM jos_datsogallery WHERE catid='5' ORDER BY id DESC");
$sorgu2=mysql_query("SELECT imgoriginalname FROM jos_datsogallery WHERE catid='6' ORDER BY id DESC");
echo '<gallery>
        <album lgPath="http://bulancakatakoy.com/components/com_datsogallery/img_pictures/" tnPath="http://bulancakatakoy.com/components/com_datsogallery/img_thumbnails/" title="Album title" description="Album description" tn="album1/preview.jpg">';
while($sonuc=mysql_fetch_assoc($sorgu)){          
echo '<img src="'.$sonuc["imgoriginalname"].'"  caption="l" link="" target="_blank" pause="" />
';
}          
        echo '</album>
        <album lgPath="http://bulancakatakoy.com/components/com_datsogallery/img_pictures/" tnPath="http://bulancakatakoy.com/components/com_datsogallery/img_thumbnails/" title="Album title" description="Album description" tn="album1/preview.jpg">';
while($sonuc2=mysql_fetch_assoc($sorgu2)){       
echo '<img src="'.$sonuc2["imgoriginalname"].'"  caption="l" link="" target="_blank" pause="" />
';
}          
        echo '</album>
</gallery>';
?>