if (document.images) 
{
   img1 = new Image();
   img2 = new Image();
   img3 = new Image();
   img4 = new Image();
   img5 = new Image();
   img6 = new Image();
   img7 = new Image();   
   img1.src = "images/nav_r1_c1_f2.jpg";
   img2.src = "images/nav_r2_c1_f2.jpg";
   img3.src = "images/nav_r4_c1_f2.jpg";
   img4.src = "images/nav_r6_c1_f2.jpg";
   img5.src = "images/nav_r7_c1_f2.jpg";
   img6.src = "images/nav_r8_c1_f2.jpg";
   img7.src = "images/nav_r9_c1_f2.jpg";    
}