function makeRequest(url,callback) {
    var http_request = false;
    
    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('Giving up :( Cannot create an XMLHTTP instance');
        return false;
    }
    http_request.onreadystatechange = function(){
        if (http_request.readyState == 4) {
            if (http_request.status == 200) {
                var objJson= http_request.responseText.evalJSON();
                callback(objJson);
            } else {
                alert('Ocorreu um problema de comunicação com o servidor.');
                return false;
            }
        }

    }
    http_request.open('GET', url, true);
    http_request.send(null);

}