There is a Prolog course (at Birmingham University) available over the web at
http://www.cs.bham.ac.uk/˜pjh/prolog_course/se207.html
This site also has information about other public domain Prologs.
And another by Patrick Blackburn, Johan Bos and Kristina Striegnitzat called ‘Learn Prolog Now!’ at
http://www.learnprolognow.org/lpnpage.php?pageid=online
Amzi!’s site provides several Prolog learning aids:
http://www.amzi.com/products/learning_products.htm
There is also a guide to Prolog programming at
http://kti.ms.mff.cuni.cz/˜bartak/prolog/index.html
Finally, the following contains links to all kinds of logic programming resources:
http://www.whoishostingthis.com/resources/prolog/