if (document.images)
{
  preload_image_object = new Image();
  // set image url
  image_url = new Array();
  image_url[0] = "/english/images/home/btn_corp_open_on.gif";
  image_url[1] = "/english/images/home/btn_corp_open_out.gif";
  image_url[2] = "/english/images/home/btn_recruitment_on.gif";
  image_url[3] = "/english/images/home/btn_recruitment_out.gif";
  image_url[4] = "/english/images/home/btn_insurance_on.gif";
  image_url[5] = "/english/images/home/btn_insurance_out.gif";
  image_url[6] = "/english/images/home/btn_corp_open02.gif";
  image_url[7] = "/english/images/home/btn_ecruitment02.gif";
  image_url[8] = "/english/images/home/btn_insurance02.gif";

   var i = 0;
   for(i=0; i<=8; i++) 
     preload_image_object.src = image_url[i];
}