var rightclickmessage = "Please don't right-click this page!";
function rtclickcheck(keyp){
  if (navigator.appName == "Netscape" && keyp.which == 3) 
  {
    alert(rightclickmessage);
    return false;
  }
  if (navigator.appVersion.indexOf("MSIE") != -1 && (event.button == 2 || event.button ==3)) 
  {
    alert(rightclickmessage);
    return false;
  }
}
document.onmousedown = rtclickcheck;