Эдди,
<!DOCTYPE HTML>
<html>
<head>
<title>Changer</title>
<meta charset="utf-8">
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js"></script>
</head>
<body>
<a href="">Открыть/закрыть</a>
<div style="height: 30px; overflow:hidden; background-color:green;">
а<br/>
б<br/>
в<br/>
г<br/>
д<br/>
е<br/>
ж<br/>
з<br/>
и<br/>
к<br/>
л<br/>
м<br/>
н<br/>
</div>
<script type="text/javascript">
$('a').click(function () {
var next = $(this).next(),
height = next.height() < next[0].scrollHeight ? next[0].scrollHeight : '30px';
next.stop().animate({'height': height}, 500);
return false;
});
</script>
</body>
</html>