CommDlg - my own messages?

(Windows programmer, BP 7.0)

I am using the 'commdlg' unit in such a way as Borland used
it in his 'chess' example.
I.E. i am using a unit 'owlcmdlg' or something like that.

1. How to force the appearing dialog to show my own messages
   in case an error occurs?
   For instance, I want the dialog to ask for overwriting
   files ('GetSaveFileName'). And it does, using his own
   message box. How to force it to use my own message box,
   or my own message at least?
2. How to write a silmilar unit called e.g. 'owlmsg',
   displaying 'WinProcs' messages as OWL Dialogs?

Yours DW.