//ブラウザのバージョンチェック
function checkVersion()
{
  var appVer=parseInt(navigator.appVersion);
  var isNC=(document.layers && (appVer >= 4)); // NN 4.0 or later
  var isIE=(document.all    && (appVer >= 4)); // IE 4.0 or later
  return (isNC || isIE);
}

//画像を先読みする
function preloadImg()
{
  if(checkVersion()){
    if(document.images){
      var imgName = preloadImg.arguments[0];
      var cnt;
      swImg[imgName] = new Array;
      for(cnt = 1; cnt < preloadImg.arguments.length; cnt++){
        swImg[imgName][cnt-1] = new Image();
        swImg[imgName][cnt-1].src = preloadImg.arguments[cnt];
      }
    }
  }
}

// Imageオブジェクトを探す
function findImg(doc, imgName)
{
  for(var i=0; i < doc.layers.length; i++){
    var img = doc.layers[i].document.images[imgName];
    if(!img)
      img = findImg(doc.layers[i], imgName);
    if(img)
      return img;
  }
  return null;
}

// 画像を入れ換える
function swapImg(imgName, imgNumber)
{
  if(checkVersion()){
    var imgSrc = swImg[imgName][imgNumber].src;
    if(document.images && imgSrc){
      var img = document.images[imgName];
      if(!img)
        img = findImg(document, imgName);
      if(img)
        img.src = imgSrc;
    }
  }
}

var swImg;
swImg=new Array;