Well, I think I figured it out and I thought that I'd put this tidbit in for anyone else who may have the problem...

On the page /includes/modules/additional_images.php, There is a line that reads

$list_box_contents[$row][$col] = array('params' => 'class="additionalImages centeredContent back"' . ' ' . 'style="width:' . $col_width . '%;"',

That % sign at the end was the problem. I just removed it (Of course, with a backup of the original file- just in case). The images aren't perfect (yet) but at least they are next to each other and the best part is- I don't think that I broke anything else!

Nancy