[plt-scheme] Hierarchy to save a file??

Hi everybody!
I'm writting a little program to draw diagram and I would like to have
the hierarchy (arborescence? in french...) in the frame "do you want
to save your file?"... And also "open a file". Do you know how to do
this please?
I have found function which deals with directory, like (directory-list
(current-directory)) for example, but I would like to have a graphical
interface (with the possibility of going from a directory to another,
cliking on a file ... like a real program!)
Thank you for helping me! (and sorry for the grammar mistakes, I'm
french)
Antoine