Cropping of gallery thumbnail images

Hi, I'm currently making a website for an arts-based charity, and I'm using imagefield gallery to show the artwork. Great module by the way. The artists don't want the images of their artwork to be cropped in the gallery thumbnails (fussy, I know), and I'm having a few issues.

I've made an Imagecache preset to resize the image to the thumbnail size, currently 120px in height, and an arbitrary width, depending on the picture. However Imagefield Gallery requires a fixed width and height – I've currently set it to 120x120px. However, this means that when an image is narrower than 120px, there is loads of white space between that thumbnail and the next one.

You can see an example of that happening here: http://79.170.40.163/actionspace.org/artists/artist-tutors/liz-emtage

So what I'm asking (in quite a roundabout way) is, is it possible to get the thumbnail to take it's dimensions from the image? Or is there a way of getting Imagefiled Gallery to take it's thumbnail dimensions from the preset settings in imagecache?

Thanks!