modifying file-selection-dialogue widget

["Chaitanya RD Kulkarni" <cboom rediffmail com>]

Hi!
I am trying to add a few buttons(with appropriate signal handlers) to the default FileSelection widget. i first created a window, then the required buttons, & then i used a container. i added the buttons to it & the fileselection widget too. it didn't work. the program compiled, but in the output, 
1.a window : with the button & empty space that should be sufficient for fileselection widget &
2.the fileselection widget, separated from this window 
were displayed. 
how to modify the default fileselection widget???
anubody knows?
-chaitanya.