if (document.images)
       {
	   		 img1on = new Image();  
	         img1on.src = "images/nav/1_roll.gif";
             img2on = new Image();  
	         img2on.src = "images/nav/2_roll.gif";
			 img3on = new Image();  
	         img3on.src = "images/nav/3_roll.gif";
			 img4on = new Image();  
	         img4on.src = "images/nav/4_roll.gif";
			 img5on = new Image();  
	         img5on.src = "images/nav/5_roll.gif";
			 img6on = new Image();  
	         img6on.src = "images/nav/6_roll.gif";
			 img7on = new Image();  
	         img7on.src = "images/nav/7_roll.gif";
			
			 img1off = new Image();  
	         img1off.src = "images/nav/1.gif";
	         img2off = new Image();  
	         img2off.src = "images/nav/2.gif";
			 img3off = new Image();  
	         img3off.src = "images/nav/3.gif";
			 img4off = new Image();  
	         img4off.src = "images/nav/4.gif";
			 img5off = new Image();  
	         img5off.src = "images/nav/5.gif";
			 img6off = new Image();  
	         img6off.src = "images/nav/6.gif";
			 img7off = new Image();  
	         img7off.src = "images/nav/7.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");  
              }
      }