var Mac= navigator.userAgent.indexOf("Mac") != -1 ?tru:false;
 function mdown(e) {
   if (navigator.appName == "Microsoft Internet Explorer") {
     if (event.button ==2 || ( Mac && (event.ctrlKey || event.keyCode==91))) {
     return false;
  }
}
 else if (navigator.appName == "Netscape") {
       if (e.which == 3 || e.modifiers == 2 || e.ctrlKey) {
           return false;
   }
}
}

if (document.all) {
     document.onmousedown =mdown;
     document.onkeydown = mdown;
  }
  else if (document.layers)  {
     window.captureEvents(Event.MOUSEDOWN | Evenet.KEYDOWN | Event.modifiers);
     window.onmousedown = mdown;
     window.onkeydown =mdown;
 }
 else if (navigator.userAgent.indexOf("Netscape6") != -1) {
          document.onmouseup =mdown;
          document.onkeydown =mdown;
   }