xmlHttp = null;
xmlHttpInstantiated = false;

/* Start XHR */
function StartXHR() {
    if(xmlHttpInstantiated) return; /* Kvůli IE se musí furt znova zavádět */
    if(window.ActiveXObject) {
        xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
    } else if(window.XMLHttpRequest) {
        xmlHttp = new XMLHttpRequest();
        xmlHttpInstantiated = true;
    }
}