if (document.images)
   {
     image_off= new Image(68,52);
     image_off.src="images/nav_off.jpg";  

     image2= new Image(68,52);
     image2.src="images/nav_home.jpg";
     image3= new Image(68,52);
     image3.src="images/nav_login.jpg";  
     image4= new Image(68,52);
     image4.src="images/nav_contact.jpg";   
   }

function change1(picName,imgName)
 {
   if (document.images)
    {
      imgOn=eval(imgName + ".src");
      document[picName].src= imgOn;
    }
 }