Cropped thumbnail in gallery post

Hello and thank you for this awesome theme.
I have a small issue with the gallery post, I would like to have something like that http://demo.onedesigns.com/pinboard/?p=174 meaning squared cropped thumbnails instead of full dimension thumbnails. Do I have to set that up in the thumbnails option?

Another question, my gallery looks like that http://arctic-mood.com/try3/ I would like to know if there is an easy (or no excessively hard) way of justifying the pictures. I would like the last picture of the first row to be centered in width and the last picture of the second row to be centered in height.

Thank you very much