function ajaxXHR() {
    var xhr = null;
    if (window.XMLHttpRequest || window.ActiveXObject) {
        if (window.ActiveXObject) {
            try {xhr = new ActiveXObject("Msxml2.XMLHTTP");}
            catch(e) {xhr = new ActiveXObject("Microsoft.XMLHTTP");}
        }
        else xhr = new XMLHttpRequest();
    } else return null;
    return xhr;
}

function ajaxLoad(req_url, data)
{
    var xhr = ajaxXHR();
    if (xhr == null) {
        alert("ajaxLoad(): XMLHTTPRequest isn't supported by your browser.");
        exit(); //it will stop the script's execution because exit() isn't recognized by the interpreters.
    }

    xhr.open("POST",req_url,false);
    xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");

    xhr.send(data);
    if (xhr.readyState == 4 && (xhr.status == 200 || xhr.status == 0)) return xhr.responseText;
}