[setishock]

You have to go after the thumb image itself. Not the container. If you resize the container, like you found, it cuts off parts of the image and/or text.
Here's the formula they use also found in the album.css

#thumbnails li .picture {
	display:block;
	width:{vb:math {vb:raw vboptions.attachthumbssize}+8}px;
	height:{vb:math {vb:raw vboptions.attachthumbssize}+8}px;
	padding:{vb:stylevar padding};
}

Pop this in to your additional.css and try changing the formulas to fixed amounts.