if (document.images) { 
           nav1on = new Image (140,20);
           nav1on.src = "/images/nav_imaging_on.gif";
           nav2on = new Image (140,20);
           nav2on.src = "/images/nav_photo_on.gif";
           nav3on = new Image (140,20);
           nav3on.src = "/images/nav_video_on.gif";
           nav4on = new Image (140,20);
           nav4on.src = "/images/nav_illus_on.gif";
           nav5on = new Image (140,20);
           nav5on.src = "/images/nav_web_on.gif";

           nav1off = new Image (140,20);
           nav1off.src = "/images/nav_imaging_off.gif";
           nav2off = new Image (140,20);
           nav2off.src = "/images/nav_photo_off.gif";
           nav3off = new Image (140,20);
           nav3off.src = "/images/nav_video_off.gif";
           nav4off = new Image (140,20);
           nav4off.src = "/images/nav_illus_off.gif";
           nav5off = new Image (140,20);
           nav5off.src = "/images/nav_web_off.gif";
     }

        function img_act(imgName) {
             if (document.images) {
               imgOn = eval(imgName + "on.src");
               document [imgName].src = imgOn;
             }
        }

        function img_inact(imgName) {
             if (document.images) {
               imgOff = eval(imgName + "off.src");
               document [imgName].src = imgOff;
             }
        }