Page organization

Hi, I have two related questions.

First, is it possible to only display parent pages in the navigation? (I’m using sidebar widgets)

And second, this is what I want to do:

I want to have my portfolio page linked from the navigation (easily done) then when portfolio’s clicked I’d like to have the subpages displayed like so:

Fiction
– Sub page 1
– Sub page 2
– Sub page 3

Letters
– Sub page 1
– Sub page 2
– Sub page 3

I was wondering if there was a way to automate this proccess. Letters & Fiction being sub pages off of Portfolio as well.

Thanks so much!