Event.observe(window, 'load', initLabelHover );

function initLabelHover() {
  $$('.label img').each( function(labelImg) {
    var normalState = labelImg.src;
    var hoverState = labelImg.src.substr(0,labelImg.src.length-4)+"_hi.gif";
    Event.observe(labelImg, 'mouseover', function(e) { this.src = hoverState; });
    Event.observe(labelImg, 'mouseout', function(e) { this.src = normalState; });
  })
}