var myXML:XML;
var myLabel:String;
var mySource:String;
var myData:String;

// first we load the external XML file 
var xmlLoader:URLLoader  = new URLLoader();
xmlLoader.load(new URLRequest("filename.xml"));
xmlLoader.addEventListener(Event.COMPLETE, handleMyData);

// then we stick it into our XML object and do stuff with it
function handleMyData(myEvent:Event):void {
	myXML = new XML(xmlLoader.data);
	popList();
}

function popList():void {
	for (var i:uint=0; i<myXML.children().length(); i++) {
		myLabel  = myXML.rockItem[i].rockName;
		mySource = myXML.rockItem[i].image;
		myData = myXML.rockItem[i].rockDescrip;
		thumbnails_tl.addItem( { label:myLabel, source:mySource, data:myData } );
	}
}
