I had Finale Notepad installed on my old computer, but the hard drive crashed. I haven't installed Finale Notepad on my new computer yet-- or rather, on my new external drive, since I'm trying to avoid filling up the internal drive the way I did on my old computer.
Anyway, you should be able to set the desired instrument for each track-- that is, each staff or musical part-- by choosing the Bank and Program for each part.
Which version of Finale is it?