procedure TTrayIcon.ShowMainForm;
begin
  with Application do
    begin
      ShowWindow(Handle, SW_SHOW);

      //maximieren
      Restore;

      //Haupt-Form anzeigen
      MainForm.Show;

      //in den Vordergrund bringen
      BringToFront;
    end;
end;

procedure TTrayIcon.HideMainForm;
var
  hwndOwner: HWnd;

begin
  with Application do
    begin
      //minimieren
      Minimize;

      //Haupt-Form verstecken
      MainForm.Hide;

      ShowWindow(Handle, SW_HIDE);

      //Icon aus der Taskleiste verstecken
      hwndOwner := GetWindow(Handle, GW_OWNER);
      ShowWindow(hwndOwner, SW_HIDE);

      //für Windows 2000
      ShowWindowAsync(hwndOwner, SW_HIDE);
      ShowWindowAsync(Handle, SW_HIDE);
    end;
end;