Navigation links and thumbnail shown on single images… why?

Yea i noticed this common issue among lightbox scripts. It technically isnt the fault of this plugin but the underlying scripts it uses. For whatever reason these lighbox script designer tend to forget obvious things like that (ie. turning off the arrows when there is only 1 image in the gallery).

Although i no longer use this plugin, instead preferring to deal with the lightbox script directly, you should be able to resolve your problem either by a jquery command or, depending on what the prettyphoto script makes available, you could do so with some css trickery. I have not worked with prettyphoto (only one of the others).