[wirehopper]

They're using jQuery. All the documentation is at jQuery: The Write Less, Do More, JavaScript Library

Code:

<script type="text/javascript" src="/javascript/jquery.js"></script>
<script type="text/javascript" src="/javascript/jquery.ui.js?20081124"></script>
<script type="text/javascript" src="/javascript/jquery.domec.js"></script>
<script type="text/javascript" src="/javascript/jquery.dimensions.min.js"></script>

You can probably copy the code from aviary and modifiy it for your needs.