function initRollOverImages() {
  var image_cache = new Object();
  $("img.over").each(function(i) {
    var imgsrc = this.src;
    var dot = this.src.lastIndexOf('.');
    var imgsrc_on = this.src.substr(0, dot) + '_on' + this.src.substr(dot, 4);
    image_cache[this.src] = new Image();
    image_cache[this.src].src = imgsrc_on;
    $(this).hover(
      function() { this.src = imgsrc_on; },
      function() { this.src = imgsrc; });
  });
}

function initRollOverImages2() {
    var image_cache = new Object();
    var $target = $("img.parents").attr("src");
    $("img.hover").each(function(i) {
        var imgsrc = $target;
        var dot = $target.lastIndexOf('.');
        var imgsrc_on = $target.substr(0, dot) + '_on' + $target.substr(dot, 4);
        image_cache[$target] = new Image();
        image_cache[$target].src = imgsrc_on;
        $(this).hover(
            function() { $("img.parents").attr({src : imgsrc_on}) ; },
            function() { $("img.parents").attr({src : imgsrc   }) ; });

    });
}

$(document).ready(initRollOverImages);
$(document).ready(initRollOverImages2);