I tried out the snapGallery script (see the last link below) – and yeah, it does exactly what I want. you have to get your pictures set up first, and I’m not entirely happy with the way it handles the CSS, but other than that….
I might see if I can figure out the scripting just enough to make it link to an external stylesheet, and maybe to make the html a little more structurally meaningful. but that’s just geeky fun. 🙂