How can I create a guitar rhythm or Piano Rhythm in the plug ins/composer's assistant/scoring & arranging/rhythm generator window?

 

                                       I only play the guitar and not drums or the piano. I can notate melody notes for a guitar stave and add extra blank staves for a guitar rhythm stave as well as bass guitar and drum staves. But how do you create rhythm in these staves going into Plug ins/scoring & arranging/composer's assistant/rhythm generator window? I only see instrument selections available for DRUM TYPES only? How can I choose guitar or bass guitar as a rhythm choice in one of these instrument boxes.? I have the Finale 2006 program. Please help. Thank you