As Don suggested code modifications can be discussed on the hack site.
I will give you a hint that you need to look in the actual sidebar main open template.
Look for the display_gallery and note the last two numbers 1,1 try 1,4
oh and on a side note, the large thumbnails also make the graphic browser all but unusable. Anyway to restrict it to just three instead of five photos?
Look at your admin options. You can control thumb size. You can control how many images to show. You can control how many columns to have whether it be 3 4 5 or 6