if(document.images) {
 var imgs = new Array();
 imgs[1] = new Image();  imgs[1].src = "http://www.geo-power.co.jp/common/menu1u.jpg";
 imgs[2] = new Image();  imgs[2].src = "http://www.geo-power.co.jp/common/menu2u.jpg";
 imgs[3] = new Image();  imgs[3].src = "http://www.geo-power.co.jp/common/menu3u.jpg";
 imgs[4] = new Image();  imgs[4].src = "http://www.geo-power.co.jp/common/menu4u.jpg";
 imgs[5] = new Image();  imgs[5].src = "http://www.geo-power.co.jp/common/menu5u.jpg";
 imgs[6] = new Image();  imgs[6].src = "http://www.geo-power.co.jp/common/menu6u.jpg";
 imgs[7] = new Image();  imgs[7].src = "http://www.geo-power.co.jp/common/menu7u.jpg"; 
} 

function chgimg(id, imgname) {
 if(document.images) {
  if(imgs[imgname]) {
    document.images[id].src = imgs[imgname].src;
  }
  else {
    document.images[id].src = imgname;
  }
 }
}