import flash.events.Event;
import flash.net.URLLoader;
import flash.net.URLRequest;
import flash.net.URLVariables;
import flash.net.URLRequestMethod;

var urlLoader:URLLoader = new URLLoader ();
var urlRequest:URLRequest = new URLRequest ('whatever.php');
var urlVars:URLVariables = new URLVariables ();

urlVars.folder = 'path/to/folder';
urlRequest.data = urlVars;
urlRequest.method = URLRequestMethod.POST;

urlLoader.addEventListener (Event.COMPLETE, onComplete);
urlLoader.load (urlRequest);

function onComplete (evt:Event) : void {
    var xml:XML = XML (urlLoader.data);
    trace (xml);
}