function ajax(url, doc, container){
	
	//if(ajax_disabled) return(false);
	
	if(url.indexOf(".") == -1) url += ".html";
	
	url = "content/"+url;
	
	ajax_disabled = true;
	
	if(container == undefined) container = "content";

	current_page = url;
	//current_level = level;
	
	var contenedor = doc.getElementById(container);
	
	var xmlHttpReq = false;
    var self = this;
    // Mozilla/Safari
    if (window.XMLHttpRequest) {
        xmlHttpReq = new XMLHttpRequest();
    }
    // IE
    else if (window.ActiveXObject) {
        xmlHttpReq = new ActiveXObject("Microsoft.XMLHTTP");
    }
	
	
    xmlHttpReq.open('POST', url, true);
    xmlHttpReq.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
	
    xmlHttpReq.onreadystatechange = function() {
		ajax_disabled = false;
		
		contenedor.innerHTML = "loading...";
		
        if (xmlHttpReq.readyState == 4) {
            contenedor.innerHTML = xmlHttpReq.responseText;
        }
    }
	
    xmlHttpReq.send(null);
	
}

function clearLeftColumn(){
	$$("left").innerHTML = "";
}