var on = new Array();
var off = new Array();

function preload() {
  var imgdir='/i/';
  for (var i=0; i<arguments.length; i++) {
    image = arguments[i];
    on[image] = new Image();
    off[image] = new Image();
    imgon = imgdir + image + '_h.gif';
    imgoff = imgdir + image + '.gif';
    on[image].src = imgon;
    off[image].src = imgoff;
  }
}

function over(img) {
  document.images[img].src = on[img].src;
}

function out(img) {
  document.images[img].src = off[img].src;
}