вот, как вариант:
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<title>123</title>
<style type="text/css">
body
{
margin: 0px;
padding: 0px;
}
.block
{
width: 400px;
border: 1px solid black;
}
</style>
</head>
<body>
<div class="div1">
<div class="div2 block" style="height: 1000px;"></div>
</div>
<script type="text/javascript" src="http://code.jquery.com/jquery-1.10.2.min.js"></script>
<script type="text/javascript">
var div1 = $('.div1');
var div2 = $('.div2');
var height = 150;
$(window).scroll(function()
{
if ($(this).scrollTop() == 0)
{
$(div1).prepend('<div class="block" style="height: ' + height + 'px;">123</div>');
height += 20;
if (height > 300)
height = 100;
var h = $(div1).children().eq(0).height();
$(window).scrollTop(h);
}
});
</script>
</body>
</html>