function SwitchFilterGroup(f,groupNum)
{
  f = document.forms[document.forms.length-1];
  for(var i =0; i < f.elements.length; i++)
  {
   element = f.elements[i];
   if(element.type != "checkbox") continue;
   id = element.id;
   if(id.substr(0,6) !="Filter")  continue;
   if(id.substr(6,1) !=groupNum)  continue;
   if(element.checked)  element.checked = false;
                else	element.checked = true;
  }
}