var _imgs = new Array();
function preLoad(){
  for (x=0; x<preLoad.arguments.length; x++){
    _imgs[x] = new Image();
    _imgs[x].src = preLoad.arguments[x];
  }
}

preLoad("./images/about_up.png","./images/about_down.png");
preLoad("./images/brokerage_down.png","./images/brokerage_up.png");
preLoad("./images/logistics_up.png","./images/logistics_down.png");
preLoad("./images/contact_up.png","./images/contact_down.png");

function toggleButton(_name,_dir) {
  _imgName = _name + "_link";
  _imgSrcUp = "./images/" + _name + "_up.png";
  _imgSrcDown = "./images/" + _name + "_down.png";
  document.images[_imgName].src = "./images/" + _name + "_" + _dir + ".png";
  //alert(_imgName);
  //alert(document.images[_imgName].src);
  //if(document.images[_imgName].src == _imgSrcUp) {
  //  document.images[_imgName].src = _imgSrcDown;
  //} else {
  //  document.images[_imgName].src = _imgSrcUp;
  //}
}