I think the modulelist looks very narrow, and that we could widen it somewhat. I don't know if it would help in this example, but I would say we could widen it by 50% without it looking bad. Also, in your example, there is a vertial scrollbar. How does it look if you stretch the dialog vertically so much that the scrollbar disappears? Maybe we should dynamically widen the module list when the scrollbar appears, so that the available width stays the same.
I can see Jerome's point, that if we make the module list horizontal, the problem would be less severe, but I kinda like the vertical approach. It is almost a standard. Most programs that have a main window and then a minor window controlling content of the main window will have the 'controlling' window to the left: Gmail, which I'm typing in now (and any other mail client), qt creator/designer, netbeans, eclipse, pcmanfm (!), etc, etc.