if (document.images) {
  nav_loc00 = new Image(); nav_loc00.src = "images/nav00_alt_loc.gif";
  nav_loc01 = new Image(); nav_loc01.src = "images/nav01_alt_loc.gif";
  nav_loc02 = new Image(); nav_loc02.src = "images/nav02_alt_loc.gif";
  nav_loc03 = new Image(); nav_loc03.src = "images/nav03_alt_loc.gif";
  nav_loc04 = new Image(); nav_loc04.src = "images/nav04_alt_loc.gif";
  nav_loc05 = new Image(); nav_loc05.src = "images/nav05_alt_loc.gif";
}