Hello Sarah. Andy is right - the completion boxes have only been available since Moodle 2.0 out Novemeber 2010. Your Moodle is indeed very old and it would be infinitely better if you could upgrade. You could consider the checklist for Moodle 1.9 here (although I can't really recommend anything so old on an unsupported Moodle version)
I wonder if a free MoodleCloud site would help?