function on() { this.src = this.src.replace(".jpg", "_h.jpg"); }
function off() { this.src = this.src.replace("_h.jpg", ".jpg"); }
function boot() {
  var eles = document.getElementById('nav').getElementsByTagName('img');
  for (var i = 0; i < eles.length; i++) {
    eles[i].onmouseover = on;
    eles[i].onmouseout = off;
  }
  var eles = document.getElementById('sidebar').getElementsByTagName('img');
  for (var i = 0; i < eles.length; i++) {
    if (eles[i].className.indexOf('rollover') > -1) {
      eles[i].onmouseover = on;
      eles[i].onmouseout = off;
    }
  }
}