I get a JS error and I can't figure out how to fix it.

When my page loads up, IE7 notifies me of a run time error. In addition, my Firebug on Firefox warns me of an error:

$ is not defined

(?)

[Break on this error] $(document).ready(function() { $(a#sin...Out': 300, 'overlayShow': false }); }); 

When I go to the lines in question its this:

<script type=text/javascript src=/templates/magazeen/js/jquery/jquery.dropdown.js></script>

    <script type=text/javascript>

    $(document).ready(function() { $(a#single_image).fancybox(); $(a#inline).fancybox({ 'hideOnContentClick': false }); $(a.group).fancybox({ 'zoomSpeedIn': 300, 'zoomSpeedOut': 300, 'overlayShow': false }); });

    </script>

Any help please.