- Na seo Private declare a procedure abaixo:

private
  procedure WMMove(var Msg: TWMMove); message WM_MOVE;
- Abaixo da palavra implementation escreva a procedure abaixo:

procedure TForm1.WMMove(var Msg: TWMMove); 
begin
  if Left < 0 then
  Left := 0;
  if Top < 0 then
  Top := 0;
  if Screen.Width - (Left + Width) < 0 then
  Left := Screen.Width - Width;
  if Screen.Height - (Top + Height) < 0 then
  Top := Screen.Height - Height;
end;