function swtch(num, imgname)
  {
    if(document.images)
      document[imgname].src = img[num].src;
  }

imgsrc = new Array();

imgsrc  [0] =  "./img_main/m01.jpg",
imgsrc  [1] =  "./img_main/m01_over.jpg",
imgsrc  [2] =  "./img_main/m02.jpg",
imgsrc  [3] =  "./img_main/m02_over.jpg",
imgsrc  [4] =  "./img_main/m03.jpg",
imgsrc  [5] =  "./img_main/m03_over.jpg",
imgsrc  [6] =  "./img_main/m04.jpg",
imgsrc  [7] =  "./img_main/m04_over.jpg"

if (document.images != null)
  {
  img = new Array();
  for (i = 0; i < imgsrc.length; i++)
    {
    img[i] = new Image();
    img[i].src = imgsrc[i];
    }
  }