I don't know Joomla, but I do know Drupal which is similar in some respects.
In Drupal, I created a block and added this code to the block:
Code:
<script language="JavaScript"
src="http://api.radioreference.com/js/?key=xxxxxxxx&feedId=yyyy&as=0&width=80px">
</script>
The trick in Drupal is that you have to tell it that the block contains HTML otherwise Drupal will try to display it as formatted text and that doesn't work because of the Javascript call.
With the block created, it's then a matter of assigning the block to a region on the page.
Don't know if this helps, but it may spark some thinking.