>>AFIAK, you can't display an MDI child form as a modal window.
Right -- generally, you call a completely different form (not a child MDI form) for modal forms, even in an MDI app. In a sense, this is exactly what you are doing with, say, a Messagebox.
The whole problem with the world is that fools and fanatics are always so certain of themselves, but wiser people so full of doubts. - Bertrand Russell