If you want bigger thumbnails on your site then you would increase the thumbnail size in the upload options in the admin of your gallery. You can not have bigger thumbnails one area and smaller somewhere else. The thumbnail size is the thumbnail size the program creates. I responded in your other thread where you where talking about category avatars and I explained how they are half the size of a thumbnail. Your overall thumbnails though are the size you set. Your default thumbnail size is 100 pixel threshold. If you want 200 pixel thumbnails then you set that.
A community photo gallery - Pet&Pet Gallery