Help: Dialog box

Hi all,

I have created a xpcom component (using c++) that will run when
mozilla start.  However, I need to pop up a dialog box or window with
some buttons in it at some occassion.

Does any one knows what should I do to at least create a dialog box or
window?  Can I avoid XUL?  Which source file under mozilla src tree is
the relevant one that I should refer?

yueweng