procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
const
  SC_DRAGMOVE = $F012;
  WM_SYSCOMMAND = $0112;
begin
  ReleaseCapture;
  Perform(WM_SYSCOMMAND, SC_DRAGMOVE, 0);
end;