tot_kotoryi,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.0/jquery.min.js"></script>
<script>
$(function(){
$(".m").mouseenter(function() {
var i = $(".m").index(this);
$(".mn").stop().not($(".mn").eq(i).show()).hide()
})
})
</script>
</head>
<body>
<div class="mn" style="display:none;"> block 1</div>
<div class="mn" style="display:none;"> block 2</div>
<ul>
<li class="m"><a href="#">Menu 1</a></li>
<li class="m"><a href="#">menu 2</a></li>
</ul>
</body>
</html>