<html>
<head>
<title>test</title>
<style type="text/css">
.block {
width: 800px;
height: 300px;
background: red;
}
</style>
</head>
<body>
<button onclick="hide()">Скрыть</button>
<div id="t" class="block"></div>
<script type="text/javascript">
function hide() {
var el = document.getElementById('t');
var count = 10, i = count, width = el.offsetWidth, height = el.offsetHeight;
(function() {
if (i--) {
el.style.width = Math.round(width * i / count) + 'px';
el.style.height = Math.round(height * i / count) + 'px';
if (typeof el.style.opacity == 'string') {
el.style.opacity = i / count;
} else {
el.style.filter = 'Alpha(opacity=' + Math.round(i / count * 100) + ')';
}
setTimeout(arguments.callee, 20);
}
})();
}
</script>
</body>
</html>
Это если уж совсем без библиотек.