Thanks Dietmar. Do I understand it right that you still have to add the lines to the template? So no jQuery stuff is already loaded automatically?
What do these lines do? Are they needed when jQuery is used?
<?php
// load jquery API
require_once("jquery_api.js");
?>
<script src="<?php echo TEMPLATE_DIR; ?>/javascript.functions.js" type="text/javascript"></script>
Sorry, still confused...

What exactly is the differerence between pre-2.8 and 2.8 regarding jQuery?