While surfing some of the blogs which I haven’t subscribed to but have linked to, I found a posting on the Subscribe to Comments plugin. I promptly installed it. I still haven’t gotten OpenID to work and it has complicated the installation of my Gravatars plugin and now this plugin.
The author seems to have planned for the latter. I should try contacting him again about my problems with his plugin but it isn’t a high priority for me. It appears things have worked themselves out for the best.
WordPress needs some sort of plugin registry system.