function derecho(e)
{
    if (navigator.appName=='Netscape' && (e.which==2||e.which==2))
    {
        alert ('Right button disabled')
        return false;
    }    
      
    else if(navigator.appName=='Microsoft Internet Explorer' && (event.button==2))
    {
        alert ('Right button disabled');
                
    }
    
}
document.onmousedown=derecho;