if (document.images) {	

   	header1_on= new Image();			header1_on.src="images/header1b.gif";  
	header1_off= new Image(); 			header1_off.src="images/header1a.gif";

   	header2_on= new Image();			header2_on.src="images/header2b.gif";  
	header2_off= new Image(); 			header2_off.src="images/header2a.gif";

   	header3_on= new Image();			header3_on.src="images/header3b.gif";  
	header3_off= new Image(); 			header3_off.src="images/header3a.gif";

   }