Ограничение размеров окна

private
  { Private declarations }
  procedure WMGetMinMaxInfo(var Info: TWMGetMinMaxInfo); message wm_GetMinMaxInfo;

implementation

{$R *.DFM}

procedure TForm1.WMGetMinMaxInfo(var Info:TWMGetMinMaxInfo);
begin
  with Info.MinMaxInfo^ do
  begin
      ptMinTrackSize.x := 200;
      ptMinTrackSize.y := 100;
      ptMaxTrackSize.x := 300;
      ptMaxTrackSize.y := 200;
      ptMaxPosition.x := BoundsRect.Left;
      ptMaxPosition.y := BoundsRect.top;
  end;
  inherited;
end;