if ( document.images )
{
  home_on = new Image ( );  home_off = new Image ( );
  home_on.src = "images/home_on.gif";  home_off.src = "images/home_off.gif";

  history_on = new Image ( );  history_off = new Image ( );
  history_on.src = "images/history_on.gif";  history_off.src = "images/history_off.gif";

  events_on = new Image ( );  events_off = new Image ( );
  events_on.src = "images/events_on.gif";  events_off.src = "images/events_off.gif";

  menu_on = new Image ( );  menu_off = new Image ( );
  menu_on.src = "images/menu_on.gif";  menu_off.src = "images/menu_off.gif";

  contact_on = new Image ( );  contact_off = new Image ( );
  contact_on.src = "images/contact_on.gif";  contact_off.src = "images/contact_off.gif";

  links_on = new Image ( );  links_off = new Image ( );
  links_on.src = "images/links_on.gif";  links_off.src = "images/links_off.gif";

  gallery_on = new Image ( );  gallery_off = new Image ( );
  gallery_on.src = "images/gallery_on.gif";  gallery_off.src = "images/gallery_off.gif";
}

function button_on ( imgName )
{
  if ( document.images )
  {
    butOn = eval ( imgName + "_on.src" );
    document[imgName].src = butOn;
  }
}

function button_off ( imgName )
{
  if ( document.images )
  {
    butOff = eval ( imgName + "_off.src" );
    document[imgName].src = butOff;
  }
}