if (document.images) {	
	
	sub_about1_on = new Image();				sub_about1_on.src="images/navigation/sub_about1b.gif";  
	sub_about1_off = new Image();		 		sub_about1_off.src="images/navigation/sub_about1a.gif";  
			
   	sub_about2_on = new Image();				sub_about2_on.src="images/navigation/sub_about2b.gif";  
	sub_about2_off = new Image(); 				sub_about2_off.src="images/navigation/sub_about2a.gif";  
	
   	sub_about3_on = new Image();				sub_about3_on.src="images/navigation/sub_about3b.gif";  
	sub_about3_off = new Image(); 				sub_about3_off.src="images/navigation/sub_about3a.gif";  
	
   	sub_about4_on = new Image();				sub_about4_on.src="images/navigation/sub_about4b.gif";  
	sub_about4_off = new Image(); 				sub_about4_off.src="images/navigation/sub_about4a.gif";  
		
}