lastMenu = 0;

function showSubMenu( id )
{
  act_display = document.getElementById('subMenu_'+id).style.display;

  if ( lastMenu > 0 )
  {
    document.getElementById('subMenu_'+lastMenu).style.display = 'none';
    document.getElementById('subMenu_'+lastMenu).style.visibility = 'hidden';
  }
  
  if ( act_display == 'block' )
  {
    document.getElementById('subMenu_'+id).style.display = 'none';
    document.getElementById('subMenu_'+id).style.visibility = 'hidden';
  }
  else
  {
    document.getElementById('subMenu_'+id).style.display = 'block';
    document.getElementById('subMenu_'+id).style.visibility = 'visible';
  }

  lastMenu = id;
}