var xmlLoader:URLLoader = new URLLoader();
xmlLoader.load(new URLRequest("data/images.xml"));

xmlLoader.addEventListener(Event.COMPLETE, xmlLoaded);

function xmlLoaded(event:Event):void
{
 trace(event.target.data);
}

images.xml

<images>
 <image source="images/Image1.jpg" thumb="thumbnails/Image1.jpg">Description of image 1.</image>
 <image source="images/Image2.jpg" thumb="thumbnails/Image2.jpg">Description of image 2.</image>
 <image source="images/Image3.jpg" thumb="thumbnails/Image3.jpg">Description of image 3.</image>
 <image source="images/Image4.jpg" thumb="thumbnails/Image4.jpg">Description of image 4.</image>
</images>

actionscript

var xml:XML;
var xmlList:XMLList;
var xmlLoader:URLLoader = new URLLoader();
xmlLoader.load(new URLRequest("data/images.xml"));

xmlLoader.addEventListener(Event.COMPLETE, xmlLoaded);

function xmlLoaded(event:Event):void
{
 xml = XML(event.target.data);
 xmlList = xml.children();
 trace(xmlList.length());
}