I've searched high and low for the answer - the codex on wp_enqueue_script seems pretty simple.
The problem is when I add my custom excerpt script to my functions file, register and then enqueue it (set to place in header), the source is displayed in the header as:
<script src="http://www.olliedaw.co.uk/wp-content/themes/DawRefrigerationMilkTanks/js/excerpt.js" type="text/javascript">
Which looks correct in firebug, but it still comes up with a 404 error when I look at the script in firebug as if it can't find the file!
File name is right, and is in the right place but still cant get it to load???
themes/Daw Refrigeration Milk Tanks/js/excerpt.js