function abrirPag(valor) {  
    var url = valor;  
    xmlRequest.open("GET", url, true);  
    xmlRequest.onreadystatechange = mudancaEstado;  
    xmlRequest.send(null);  
    if (xmlRequest.readyState == 1) {  
        document.getElementById("divConteudo").innerHTML = "Carregando...";  
    }  
    return url;  
}  

function mudancaEstado() {
    if (xmlRequest.readyState == 4) {
        document.getElementById("divConteudo").innerHTML = xmlRequest.responseText;
     }
}