function ObjAjax(){
  try{return new XMLHttpRequest()}
  catch(e){try{return new ActiveXObject("Msxml2.XMLHTTP")}
  catch(e){return new ActiveXObject("Microsoft.XMLHTTP")}}
  return null;
}


function carrega(page){
	
	ajax = new ObjAjax();

	var div = document.getElementById("principal");

	ajax.onreadystatechange = function(){
    if(ajax.readyState == 1){div.innerHTML="Carregando...";}
    if(ajax.readyState == 4){div.innerHTML=ajax.responseText;}

  }
  ajax.open("GET",page,true);
  ajax.send(null);
}