I've finally figured out how people have been making these awesome slideshows:
The site is PictoBrowser, "Fast and Effortless photo galleries for your website or blog." It's free and you just need a Flickr account to use it. Very easy and fun.
This is the followup to my previous post about blacksmithing class. I had trouble logging into my Flickr account for a few days, but finally worked it out. Stupid yahoo account email address I never use. [grumble grumble]