While I agree with Dani about Power CMS and PowerStore (they do what it says on the tin) I'm not sure that PowerGallery would be the right tool, assuming that I understood your original brief.
As far as I can work out (I have it), PowerGallery doesn't at the moment support multiple logins/levels and multiple albums. It's a great little app, for a personal site, but not perhaps for what you are describing.
I would recommend SlideShowPro for Flash along with SlideShowPro Director. The licence for Director is for one site only, but it sounds like that's all you need. There are user levels of Administrator, Editor and contributor. All kinds of integration extras (external linking) and ways of 'tapping in' to the API ("to display data and images outside of SlideShowPro in your own custom front-end applications").
It handles video too.