function clickIE() {
   if (document.getElementById) return false;
}

function clickNS(e) {
   if (document.layers||(document.getElementById&&!document.getElementById))
      if (e.which==2 || e.which==3) return false;
}

if (document.layers) {
   document.captureEvents(Event.MOUSEDOWN);
   document.onmousedown=clickNS;
}else{
   document.onmouseup=clickNS;
   document.oncontextmenu=clickIE;
}