var base = "img/";

if (document.images) {            	

	img1on = new Image();   img1on.src = base + "navde_on.gif"; 
	img2on = new Image();   img2on.src = base + "navport_on.gif";
		

	img1off = new Image();  img1off.src = base + "navde_off.gif";
	img2off = new Image();  img2off.src = base + "navport_off.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");
		}
	}