if (document.layers) 
{
    document.captureEvents(Event.MOUSEDOWN);
}
document.onmousedown = noclic;

function noclic(clic) 
{
    if (navigator.appName == 'Netscape' && clic.which==3) 
    {
        //alert(mess);
    }
    else
    if(navigator.appName == 'Microsoft Internet Explorer' && event.button==2) 
    {
        //alert(mess);
    }
}