function preload() {
    if (document.images) {
        preload_image_object = new Array();
        image_url = new Array();
        image_url[0] = "../images/button_Patients.gif";
        image_url[1] = "../images/buttonH_Patients.gif";
        image_url[2] = "../images/button_Physicians.gif";
        image_url[3] = "../images/buttonH_Physicians.gif";
        image_url[4] = "../images/button_ClinicalTrials.gif";
        image_url[5] = "../images/buttonH_ClinicalTrials.gif";
        image_url[6] = "../images/button_Products.gif";
        image_url[7] = "../images/buttonH_Products.gif";
        image_url[8] = "../images/button_CustomerService.gif";
        image_url[9] = "../images/buttonH_CustomerService.gif";
        image_url[10] = "../images/button_refill.gif";
        image_url[11] = "../images/buttonU_refill.gif";
        image_url[12] = "../images/button_viewprescriptions.gif";
        image_url[13] = "../images/buttonU_viewprescriptions.gif";
        image_url[14] = "../images/button_pharmacist.gif";
        image_url[15] = "../images/buttonU_pharmacist.gif";
        image_url[15] = "../images/BG_refill.jpg";

        for (var i = 0, limit = image_url; i < limit; i++) {
            preload_image_object[i] = new Image();
            preload_image_object[i].src = image_url[i];
        }
    }
}