function sendRequest(url, callback, data) 
{ 
    // init 
    url += url.indexOf("?") >= 0 ? "&" : "?"; 
    url += "random_download_url=" + Math.random(); 
    
    if (typeof data == 'undefined') 
    { 
        var data = null; 
    } 
  
    method = data ? 'POST' : 'GET'; 
    
    // create XMLHttpRequest object 
    if (window.XMLHttpRequest) 
    { 
        var objXMLHttpRequest = new XMLHttpRequest(); 
    } 
    else 
    { 
        var MSXML = ['MSXML2.XMLHTTP.6.0', 'MSXML2.XMLHTTP.3.0', 'MSXML2.XMLHTTP.5.0', 'MSXML2.XMLHTTP.4.0', 'MSXML2.XMLHTTP', 'Microsoft.XMLHTTP']; 
        for(var n = 0; n < MSXML.length; n ++) 
        { 
            try 
            { 
                var objXMLHttpRequest = new ActiveXObject(MSXML[n]);        
                break; 
            } 
            catch(e) 
            { 
            } 
        } 
    } 
    
    // send request 
    with(objXMLHttpRequest) 
    { 
        //setTimeouts(30*1000,30*1000,30*1000,30*60*1000); 
        try 
        { 
            open(method, url, true); 
            
            if (method == 'POST') 
            { 
                setRequestHeader('Content-Type', 'application/x-www-form-urlencoded; charset=GB2312'); 
            } 
            
            send(data);            
        } 
        catch(e) 
        { 
            alert(e); 
        } 
        
        // on ready 
        onreadystatechange = function() 
        { 
            if (objXMLHttpRequest.readyState == 4) 
            { 
                callback(objXMLHttpRequest.responseText, objXMLHttpRequest.status); 
                delete(objXMLHttpRequest); 
            } 
        } 
    } 
}