var Mac   = navigator.userAgent.indexOf("Mac") != -1   ? true :
false;
        function mdown(e) {
        if (navigator.appName == "Microsoft Internet Explorer") {
                if (event.button == 2 || (Mac && (event.ctrlKey ||
event.keyCode == 91))) {
                        alert("右クリックは無効です。");
                        return(false);
                }
          } else if (navigator.appName == "Netscape") {
                if (e.which == 3 || e.modifiers == 2 || e.ctrlKey) {
                        alert("右クリックは無効です。");
                        return false;
            }
          }
        }

        function noright(){
                alert("右クリックは無効です。");
                return false;
        }


        document.oncontextmenu = noright;

        if (document.all && (Mac || ! document.getElementById)) {
                document.onmousedown = mdown;
                document.onkeydown = mdown;
        } else if (document.layers) {
                window.captureEvents(Event.MOUSEDOWN | Event.modifiers |
Event.KEYDOWN);
                window.onmousedown = mdown;
                window.onkeydown = mdown;
        } else if(navigator.userAgent.indexOf("Netscape6")!=-1){
                document.onmouseup = mdown;
                document.onkeydown = mdown;
        }