V okně, co má být v aplikaci "furt nahoře" udělej toto:

type TForm1 = class (TForm)
   ---
   private
   procedure CreateParams (var AParams: TCreateParams); override;
   ---
end;
---
---
TForm1.CreateParams (var AParams: TCreateParams);
begin
   inherited CreateParams (AParams);
   AParams.WndParent := Application.MainForm.Handle;
end;
(