function ajax() {
       if(typeof ajax._initialized == "undefined"){
           ajax.prototype.createREQ = function() {
                 var xmlHttp = false;
                 if (window.XMLHttpRequest) {
                   xmlHttp = new XMLHttpRequest();
                   if (xmlHttp.overrideMimeType) {
                       xmlHttp.overrideMimeType('text/xml');
                   }
               } else if (window.ActiveXObject) {
                   try {
                          xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
                   } catch (e) {
                          try {
                              xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
                          } catch (e) {}
                   }
               }
               if (!xmlHttp) {
                     alert('Twoja przegladarka nie obsluguje technologii Ajax! Pobierz i zainstaluj Mozilla Firefox.');
                   return false;
               }
               return xmlHttp;
           }
           ajax.prototype.requestGET = function (url, query, req) {
               var myRand = parseInt(Math.random()*99999999);
               req.open("GET", url + '?' + query + '&rand=' + myRand, true);
               req.setRequestHeader('Content-Type', 'text/html; charset=iso-8859-2');
               req.send(null);
           }
           ajax.prototype.requestPOST = function (url, query, req) {
               req.open("POST", url, true);
               req.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded; charset=iso-8859-2');
               req.send(query);
           }
           ajax.prototype.doAjax = function (url, query, callback, reqtype, getxml) {
               var myreq = this.createREQ();
               myreq.onreadystatechange = function() {
                   if(myreq.readyState == 4) {
                       if(myreq.status == 200) {
                           //usun_okienko('preload');
                           var item = myreq.responseText;
                           if(getxml == 1) {
                               item = myreq.responseXML;
                           }
                           doCallback(callback, item);
                       }
                   } else {
                       if(document.getElementById('preload') == null){
                           //preloader
                       }
                   }
               }
               if(reqtype == 'post'){
                   this.requestPOST(url, query, myreq);
               }
               else {
                   this.requestGET(url, query, myreq);
               }
           }
       }
       ajax._initialized = true;
   }
   function doCallback (callback, item) {
       eval(callback + '(item)');
   }
   var doAjax = new ajax();

if (xmlHttp.overrideMimeType) {
    xmlHttp.overrideMimeType('text/xml');
}

if (xmlHttp.overrideMimeType) {
     xmlHttp.overrideMimeType('text/plain');
}