var oPopup = window.createPopup();
function openPopup()
{
    
    var oPopBody = oPopup.document.body;
    
     mess_text = document.getElementById("ctl00_ContentPlaceHolder1_hfHelp").value;     
     oPopBody.innerHTML = "<table cellspacing=0 cellpadding=0 width=100%><tr><td style='background-image:url(../../images/elements/common/window.gif);width=301;height:201;font-family: Arial; font-size: 13px;padding: 10px;'>" + mess_text + "</td></tr></table>";
    //calc. center
    var x, y;
    x = window.screen.availWidth/2-150;
    y = 40;
    oPopup.show(x, y, 301, 201, document.body);
}