Lucky you, the D100 has a depth of field preview button! I think it’s on the front of your camera, right by the lens.
I’m not sure about the D100, but on my rebelxt I can hold the dof preview button down, then fiddle with the aperture until I see what I want. Try it out.
Of course, now that this thread is 7 months old and you’ve probably already found a great solution you’ve been using for months.