function mark_all( form_id )
{
	var form = document.getElementById( form_id ), elem;

	for( var i=0; i<form.elements.length; i++ )
	{
		elem = form.elements[i];

		if( elem.type == 'checkbox' )
			elem.checked = !form.alle.checked;
	}

	form.all.checked = !form.all.checked;
}