On your Extras page, there is a link for "iTunes CD Info" plug-in. I had CDpedia download and install it, but I can't find the command. It's supposed to be a menu plug-in, but I can't find it in a menu. Perhaps I just don't know where to look.
After restarting CDpedia, there should be an extra little menu after the Help menu. It's a small picture of a plug-in. If the automatic install does not work, you can click on the name of the plug-in on the extras page, to get a link to manual install.
