var on = new Array(); 
var off = new Array();
function preload (name, off_img, on_img) {
  off[name] = new Image();
  off[name].src = '/images/' + off_img;
  on[name] = new Image();
  on[name].src = '/images/' + on_img;
}
function roll_on  (name) { document.images[name].src = on[name].src; }
function roll_off (name) { document.images[name].src = off[name].src; window.status = ''; return true; }