This might be a totally stupid question, but...is there a way to make it possible for people who are not registered users to still be able to leave comments?
Yes, use the groups page and album properties.
http://coppermine-gallery.net/demo/cpg13x/docs/faq.htm#onlyregisteredcomments
Oy! Thank you. The sad thing is, I spend half an hour looking through this site and the faqs in search of the answer to that particular question and somehow managed to not find it eventhough it was right in front of me. ::) Now I feel incredibly stupid. But, at least I have the answer to my question. ;D