The simple answer is: if you want the images to be the same size, it is best to resize them before upload
The more advanced answer (though not supported) is: The image sizes are controlled by the gallery script.
in the ribbon light box, gallery, the following line in the gallery/ribon_lightbox.php page sets the size of the thumbnails and the large images:
$gallery = get_gallery(get_mediarss_url('gallery=' . $pg_id . '&thumb=62c&full=782p'));
thumb is set to 62c and full is set to 782p
these sizes corespoond to what is set in the admin/common/properties.php file in the resize proportional and resize cropped globals:
$GLOBALS['resize_proportional'] = array(
array('w' => 1024, 'h' => 768, 'watermark' => true),
array('w' => 782, 'h' => 481, 'watermark' => true),
array('w' => 163, 'h' => 92)
);
$GLOBALS['resize_cropped'] = array(
array('w' => 62, 'h' => 62),
array('w' => 132, 'h' => 140),
array('w' => 102, 'h' => 102),
array('w' => 42, 'h' => 42),
array('w' => 782, 'h' => 481, 'watermark' => true),
array('w' => 995, 'h' => 260, 'watermark' => true)
);
768p is set to a width of 1024 and height 768. it is a proportional setting so the images will be resized proportionally, if you wanted them to be the same size all the time, you would want to use a cropped setting, but this would mean the images would be cropped from center on resize. to have more control, you should resize before upload.
No power store does not have support for other gallery types, but they can be hand coded.
