if (document.images) {
  pic1= new Image(1,1); 
  pic1.src="images/nav1_hover.gif"; 
  pic2= new Image(1,1); 
  pic2.src="images/nav2_hover.gif"; 
  pic3= new Image(1,1); 
  pic3.src="images/nav3_hover.gif"; 
  pic4= new Image(1,1); 
  pic4.src="images/nav4_hover.gif"; 
  pic5= new Image(1,1); 
  pic5.src="images/nav5_hover.gif"; 
  pic6= new Image(1,1); 
  pic6.src="images/buy_hover.gif"; 
 }