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$(function() {
  $('#nav2 li img')
	.hover(
		function(){
			$(this).stop().animate({'marginTop':'-29px'},'fast');
		},
		function () {
			$(this).stop().animate({'marginTop':'0px'},'fast');
		}
	);
});

<ul id="nav1">
  <li><a href="#"><img src="img/nav01.gif" width="100" height="59" /></a></li>
	<li><a href="#"><img src="img/nav02.gif" width="100" height="59" /></a></li>
	<li><a href="#"><img src="img/nav03.gif" width="100" height="59" /></a></li>
	<li><a href="#"><img src="img/nav04.gif" width="100" height="59" /></a></li>
</ul>

#nav1 li {
  float: left;
	margin-left: -1px;
	width: 100px;
	height: 30px;
	overflow: hidden;
}