function Ajax(url,callback) {
        var httpRequest;
        if (window.XMLHttpRequest) { // Mozilla, Safari, ...
            httpRequest = new XMLHttpRequest();
            if (httpRequest.overrideMimeType) {
                httpRequest.overrideMimeType('text/xml');
                // See note below about this line
            }
        } 
        else if (window.ActiveXObject) { // IE
            try {
                httpRequest = new ActiveXObject("Msxml2.XMLHTTP");
                } 
                catch (e) {
                           try {
                                httpRequest = new ActiveXObject("Microsoft.XMLHTTP");
                               } 
                             catch (e) {}
                          }
                                       }

        if (!httpRequest) {
            alert('Giving up :( Cannot create an XMLHTTP instance');
            return false;
        }
        httpRequest.onreadystatechange = function() { callback(httpRequest); };
        httpRequest.open('GET', url, true);
        httpRequest.send('');

};