<!--
    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("右クリックは利用できません。");
                return(false);
            }
        } else if (navigator.appName == "Netscape") {
            if (e.which == 3 || e.modifiers == 2 || e.ctrlKey) {
                alert("右クリックは利用できません。");
                return false;
            }
        } 
    }

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