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>