isIE = document.all;
isNN = !document.all&&document.getElementById;
isN4 = document.layers;

function disableRightClick(e) {
        if (isN4) {
                if (e.which == 2 || e.which == 3) {
                        return false;
                }
        } else {
                return false;
        }

        return true;
}

if (isIE || isNN) {
        document.oncontextmenu = disableRightClick;
} else {
        document.captureEvents(Event.MOUSEDOWN || Event.MOUSEUP);
        document.onmousedown = disableRightClick;
}