function getRequest()
{
    var xRequest = null;
    if (window.XMLHttpRequest)
    {
	    xRequest = new XMLHttpRequest();
    }
    else if (typeof ActiveXObject != "undefined")
    {
	    xRequest = new ActiveXObject("Microsoft.XMLHTTP");
    }
    return xRequest;
}

var req;

function doRequest(url, callback)
{
    if (!url || url == '')
        return;
        
    req = getRequest();
    if (req != null)
    {
        req.onreadystatechange = function() {
            if (req.readyState == 4) {
                if (req.status == 200) {
                    if (callback) callback(req);
                }
            } else {
                //fail
            }
        };
        req.open("GET", url, true);
        req.send(null);
    }
}