Buttons of ModalWindow - enabled:= true / false

[I.Igor]

Hello.
How do I control the accessibility of buttons in a modal window?
In delphi, I would do something like this:

  Button1.Enabled: = ChechkBox1.Checked and (ComboBox.ItemIndex <> -1);

But in IWModalWindow Buttons is a TStringList. How do I access the properties of buttons? I've tried  like this :
var
  Button: TIWButton;
begin
  Button: = TIWButton (ModalWindow.Buttons.Objects[0]);
  Button.Enabled: = false  // Button = nil
end;
But it doesn't work.

Or not to use ModalWindow.Buttons for such cases? Just use the standard buttons taken from the palette and added inside the ModalWindow panel?