function click (e) {
    if (!e)
        e = window.event;
        if ((e.type && e.type == "contextmenu") || (e.button && e.button == 2) || (e.which && e.which == 3)) {
            if (window.opera)
                window.alert("Sorry: Diese Funktion ist deaktiviert.");
                return false;
    }
}

if (document.layers)
document.captureEvents(Event.MOUSEDOWN);
document.onmousedown = click;
document.oncontextmenu = click;