Gallery thumbnail spacing problems

I’m having trouble getting thumbnails to line up properly in galleries. Is anyone able to help?

1st example
http://chookman.id.au/wp_orchids/?page_id=325
This is done using the default WordPress gallery.
The images are mostly lined up properly, but they are all left aligned. Vertically, the portrait images should be centred in reference to the landscape ones. The caption text should be centre aligned too. I also cannot work out how to make the number of columns, dynamic, according to how wide the viewer’s browser is.

2nd example
http://chookman.id.au/wp_orchids/?page_id=57
This is done by adding the images to the page directly, with left align. However, because some of the thumbnails are a bit wider than others, the alignment is a bit off. All the thumbnails should be aligned equally. Also, the last few thumbnails take up bizarre positions for some reason, I can’t work out why.

3rd example
http://chookman.id.au/wp_orchids/?page_id=151
This is done with NextGen gallery. This would be almost perfect, except that once again, the images are not aligned properly, as they are not the same size. The centre point of each thumbnail should be the same distance from the next, so that different sized thumbnails do not ruin the alignment. Also, if there is one image in a row by itself, it should be centre aligned.

4th example
http://chookman.id.au/wp_orchids/?page_id=158
This is also done using NextGen Gallery. The alignment on this page is completely off. I would like the thumbnails displayed with each thumbnail centred horizontally in line with the one in the row above. Number of columns should depend on the width of the viewer’s browser.
Images should be aligned like they are on my old website: http://orchids.chookman.id.au/drakaea/drakaea.html