간단하게 한줄 처리도 가능한데..
저는 아래 방법을 사용합니다.

<script language="JavaScript">
<!--
document.onmouseover = function ( e ) { 
if ( !e ) e = window.event; 
var el = e.target ? e.target : e.srcElement; 
while ( el != null && el.tagName != "A" ) el = el.parentNode; 
if ( el == null ) return; 
if ( e.preventDefault ) e.preventDefault(); 
else e.returnValue = true;};
//-->
</script>
<SCRIPT LANGUAGE="Javascript">
<!--
var isNS = (navigator.appName == "Netscape") ? 1 : 0;
var EnableRightClick = 0;
if(isNS)
document.captureEvents(Event.MOUSEDOWN||Event.MOUSEUP);

function mischandler(){
  if(EnableRightClick==1){ return true; }
  else {return false; }
}

function mousehandler(e){
  if(EnableRightClick==1){ return true; }
  var myevent = (isNS) ? e : event;
  var eventbutton = (isNS) ? myevent.which : myevent.button;
  if((eventbutton==2)||(eventbutton==3)) return false;
}

function keyhandler(e) {
  var myevent = (isNS) ? e : window.event;
  if (myevent.keyCode==96)
    EnableRightClick = 1;
  return;
}

document.oncontextmenu = mischandler;
document.onkeypress = keyhandler;
document.onmousedown = mousehandler;
document.onmouseup = mousehandler;
//-->
</script>