I have mainly sorted it out.

You can change the thumbnail settings in wordpress that you have linked to in the code, therefore changing the size of the thumbnail.

If you set either the height OR width to 0 the output thumbnail will be a ratio of the value of height or width that you have set as the default value.

I have a fixed height, 150 pixels and have unselected cropping (this is mainly what my client didnt like) and it mainly works.

However now the landscape thumbnails (which now have a height less than 150 pixels) make the button appear just below it. Therefore the select buttons are not in the same horizontal location when you have portrait and landscape thumbnails side by side.

This is the only thing I have to fix now. I know I have to add a class in css with properties height 150px for ALL thumbnails so that the button is pushed down, but I am having troubles in putting it in the right location so it doesnt screw up the whole layout of the page.

I will let you know how I get on, but do you have any ideas where I can put this (if the above made sense)

Thanks,

Leon