In a new installation, images uploaded are getting onto the server (they can be called by the direct URL), but are appearing as broken images when cropped for album thumbnails or when viewing the album.

Are there any obvious initial settings or configs that I need to check or make to remedy this?

Please see
http://www.zenphoto.org/2009/03/troubleshooting-zenphoto/#10
http://www.zenphoto.org/2009/03/troubleshooting-zenphoto/#11

Thanks - I think it was the permissions on the cache folder

Cheers