Problems with thumbnails in Dynamic Content Gallery

I'm redesigning one of my blogs using Thesis Network News skin and with the Dynamic Content Gallery. So far I've managed to put things together pretty well but I'm stuck with thumbnails and would appreciate some advice from any of you who have used Thesis/DCG.

Here is where I'm at.

I have my images full URL in the Dynamic Content Gallery Metabox and they dislplay well in the slider. I have the full URL in the Post Image and Thumbnail section and it displays well inside the post proper.

If I place the URL in the thumbnail image section then I do of course get the full image which is not what I want but I don't know how to get DCG to crop it to my desired size 100x60 - I'm beginning to wonder if for every image in the slider do I have to make a second smaller image? Somehow I imagine not.

I'm quite sure the question is simple - but then all questions are simple when you know the answer.

I'm heading for the same sort of look as the Thesis Network News skin (Network News)

Do appreciate that this is a question for those with knowledge of Thesis and DCG

Kevin