if(document.images) {
   img1on = new Image();
   img1on.src = "images/welcome_on.gif";
   img1off = new Image();
   img1off.src = "images/welcome_on.gif";

   img2on = new Image();
   img2on.src = "images/aboutus_on.gif";
   img2off = new Image();
   img2off.src = "images/aboutus_off.gif";

   img3on = new Image();
   img3on.src = "images/services_on.gif";
   img3off = new Image();
   img3off.src = "images/services_off.gif";

   img4on = new Image();
   img4on.src = "images/links_on.gif";
   img4off = new Image();
   img4off.src = "images/links_off.gif";
  
   img5on = new Image();
   img5on.src = "images/contactus_on.gif";
   img5off = new Image();
   img5off.src = "images/contactus_off.gif";
   
}
function imgOn(imgName) {
   if (document.images) {
      document[imgName].src = eval(imgName + "on.src");
   }
}
function imgOff(imgName) {
   if (document.images) {
      document[imgName].src = eval(imgName + "off.src");
   }
}