function criaObjAjax() {
    if (typeof XMLHttpRequest != "undefined")
        return new XMLHttpRequest(); // Funciona para Firefox, Mozilla, Chrome, Safari, Opera, Konqueror, Nautilus, ..
    else if (window.ActiveXObject){ // P/ Funcionar no IE.
        var versoes = ["MSXML2.XMLHttp.3.0",
                       "MSXML2.XMLHttp.4.0", 
                       "MSXML2.XMLHttp.5.0",
                       "MSXML2.XMLHttp", 
                       "Microsoft.XMLHttp"]; 
        }
    for (var i = 0; i < versoes.length; i++){
        try{
            return new ActiveXObject(versoes[i]);
        }
        catch (e) {
        }
    }
    throw new Error("Seu browser nao suporta AJAX");
}