I can get add_image_size to work with my thumbnails on by posts if I post the images individually.
However add_image_size doesn't seem to work with the wp built in [gallery] thumbnails. The only thing that seems to control the thumbnails is the 'thumbnail' section of the 'media' tab in the wp-admin area.
Am I doing somehting wrong or is it that you cant control the gallery thumbnails with add_iamge_size.
Also I don't want to use plugins.