Creating a image bank for media and press, they need the imgages in high resolution, but cannot figure out where the settings are for high resolution are - or if there are any limitations.

Can any one help me out here, please?

Zenphoto is meant for websites and on the net you don't really need high print ready resolutions. Actually it is not even recommended as such images will bascially crash any server when creating the thumbnails or other layout specific images. Of course unless you have a really really powerful server.

Recommended read on basics how Zenphoto works:
http://www.zenphoto.org/news/why-are-some-of-my-thumbnails-sized-images-not-generated-why-does-zenphoto-make-my-server-crash-while-processing-images-
http://www.zenphoto.org/news/is-it-really-necessary-to-pre-cache-my-images-at-all-

You can of course access the "high resolution" images. These are called full images in Zenphoto terms. You might need to modify the theme used to access these for downloads or else (This has been covered lots of times on the forum).