function ajaxRequest()
{
    try
    {
        // Firefox, Opera 8.0+, Safari
        return  new XMLHttpRequest();
    }
    catch (e)
    {
        // Internet Explorer
        try
        {
            return new ActiveXObject("Msxml2.XMLHTTP");
        }
        catch (e)
        {
            try
            {
                return new ActiveXObject("Microsoft.XMLHTTP");
            }
            catch (e)
            {
                return false;
            }
        }
    }
}

var xmlHttp = ajaxRequest();