$(document).ready(function(){
	$('nav ul li .normal img').mouseenter(function(){
		var image = $(this).attr('src');
		image = image.split('.gif');
		hover_image = image[0]+"_sw.gif";
		$(this).attr('src',hover_image);
	});
	
	$('nav ul li .normal img').mouseleave(function(){
		var image = $(this).attr('src');
		image = image.split('_sw.gif');
		hover_image = image[0]+".gif";
		$(this).attr('src',hover_image);
	});
});