function preload()
{
prIMG1 = new Image();
prIMG1.src = "./img/bn_01_on.gif";
prIMG2 = new Image();
prIMG2.src = "./img/bn_02_on.gif";
prIMG3 = new Image();
prIMG3.src = "./img/bn_03_on.gif";
prIMG4 = new Image();
prIMG4.src = "./img/bn_04_on.gif";
}
// stImgPreload:
function stImgPreload()
{
  var appVer=parseInt(navigator.appVersion);
  var isNC=(document.layers && (appVer >= 4));
  var isIE=(document.all    && (appVer >= 4));
  if (isNC || isIE)
  {
    if (document.images)
    {
      var imgName = stImgPreload.arguments[0];
      var cnt;
      swImg[imgName] = new Array;
      for (cnt = 1; cnt < stImgPreload.arguments.length; cnt++)
      {
        swImg[imgName][stImgPreload.arguments[cnt]] = new Image();
        swImg[imgName][stImgPreload.arguments[cnt]].src = stImgPreload.arguments[cnt];
      }
    }
  }
}

// stImgFind:
function stImgFind(doc, imgName)
{
  for (var i=0; i < doc.layers.length; i++)
  {
    var img = doc.layers[i].document.images[imgName];
    if (!img) img = stImgFind(doc.layers[i], imgName);
    if (img) return img;
  }
  return null;
}

// stImgSwap:
function stImgSwap(imgName, imgSrc)
{
  var appVer=parseInt(navigator.appVersion);
  var isNC=(document.layers && (appVer >= 4));
  var isIE=(document.all    && (appVer >= 4));
  if (isNC || isIE)
  {
    if (document.images)
    {
      var img = document.images[imgName];
      if (!img) img = stImgFind(document, imgName);
      if (img) img.src = imgSrc;
    }
  }
}
var swImg; swImg=new Array;