// Esse está funcionando perfeitamente no IE
  document.oncontextmenu = function() {return false;};
  document.onselectstart = function() {return false;};
  
  function disableselect(e){
     return false
  }

     function reEnable(){
     return true
  }

     //if IE4+
     document.onselectstart=new Function ("return false")

     //if NS6
  if (window.sidebar){
     document.onmousedown=disableselect
     document.onclick=reEnable
  }