As far as I can diagnose the problem, I think you have interchanged the lines. First include JQuery and then the plugin.
<script src="http://code.jquery.com/jquery-latest.js" type="text/javascript"></script>
<script src="Islands/jquery.overscroll.js" type="text/javascript"></script>
You can check out the demo over
here[
^]
Please make sure that you are able to load the jquery.overscroll.js file. You can check it out by using FireBug (if using Firefox) or Developer Tools (If using IE) Both can be invoked by F12.