var http_request = false;
 var campo = null;
//funcao de envio de requisicao
 function enviar(url,metodo,saida) 
 {
        http_request = false;
        campo = saida
        if (window.XMLHttpRequest) 
           { // Mozilla, Safari,...
            	http_request = new XMLHttpRequest();
	            if (http_request.overrideMimeType) 
	            {
	                http_request.overrideMimeType('text/xml');
	                // See note below about this line
	            }
            }
            else if (window.ActiveXObject) 
            { // IE
	            try {
		                http_request = new ActiveXObject("Msxml2.XMLHTTP");
		            } 
		            catch (e) 
		            {
		              try {
		                    http_request = new ActiveXObject("Microsoft.XMLHTTP");
		                  }
		            catch (e) {}
	                }
            }

        if (!http_request) {
            alert('Broswer sem suporte a AJAX');
            return false;
        }

       if(metodo == "GET")
        {
	        http_request.onreadystatechange = alertContents;
	        http_request.open('GET', url, true);
	        http_request.send(null);
        } 
        else
        { 
            http_request.onreadystatechange = alertContents;
            http_request.open("POST", url, true);
            http_request.setRequestHeader("Content-Type", "application/x-www-form-urlencoded; charset=UTF-8");
            http_request.setRequestHeader("Cache-Control", "no-store, no-cache, must-revalidate");
            http_request.setRequestHeader("Cache-Control", "post-check=0, pre-check=0");
            http_request.setRequestHeader("Pragma", "no-cache");
            http_request.send(url);
        }    

 }

    function alertContents()
 {
        if (http_request.readyState < 4)
        {
        	document.getElementById(campo).innerHTML = "<img src='images/ajax.gif'>";
        }
        else
        {
	        if (http_request.readyState == 4) 
	        {
	           if (http_request.status == 200) 
	           {
                   //document.getElementById(campo).innerHTML = unescape(http_request.responseText.replace(/\+/g," "));
          	     document.getElementById(campo).innerHTML = http_request.responseText;
                   }
	           else
	           {
	              alert('Problemas, tente novamente.');
	           }
	        }
        }
 }