Ocultar aplicación en la barra de tareas.

 procedure TfrmMain.BtnHideFromTaskBarClick(Sender: TObject);
 begin
   ShowWindow( Application.Handle, SW_HIDE );
   SetWindowLong( Application.Handle, GWL_EXSTYLE,
                  GetWindowLong(Application.Handle, GWL_EXSTYLE) or
                  WS_EX_TOOLWINDOW and not WS_EX_APPWINDOW);
   ShowWindow( Application.Handle, SW_SHOW );
 end;