[Setup]
AppName=My Program
AppVersion=1.5
DefaultDirName={pf}\My Program

[Registry]
Root: HKLM; Subkey: "Software\My Company\My Program\Settings"; ValueType: string; ValueName: "InstallPath"; ValueData: "{code:GetDirPath}"

[Code]
var
  InputPage: TInputDirWizardPage;
  RadioButtons: array[0..1] of TNewRadioButton;

function GetDirPath(Param: string): string;
begin
  Result := InputPage.Values[0];
end;

procedure ShiftDirPageItem(Page: TInputDirWizardPage; Index: Integer;
  Offset: Integer);
begin
  Page.Edits[Index].Top := Page.Edits[Index].Top + Offset;
  Page.Buttons[Index].Top := Page.Buttons[Index].Top + Offset;
  Page.PromptLabels[Index].Top := Page.PromptLabels[Index].Top + Offset;
end;

procedure SetDirPageItemEnabled(Page: TInputDirWizardPage; Index: Integer;
  Enabled: Boolean);
begin
  Page.Edits[Index].Enabled := Enabled;
  Page.Buttons[Index].Enabled := Enabled;
  Page.PromptLabels[Index].Enabled := Enabled;
end;

procedure RadioButtonClick(Sender: TObject);
begin
  SetDirPageItemEnabled(InputPage, 0, Sender = RadioButtons[1]);
end;

procedure InitializeWizard;
begin
  InputPage := CreateInputDirPage(wpWelcome, 'Caption', 'Description',
    'SubCaption', False, '');
  InputPage.Add('Prompt');

  RadioButtons[0] := TNewRadioButton.Create(InputPage);
  RadioButtons[0].Parent := InputPage.Surface;
  RadioButtons[0].Left := 0;
  RadioButtons[0].Top := 0;
  RadioButtons[0].Width := InputPage.SurfaceWidth;
  RadioButtons[0].Checked := True;
  RadioButtons[0].Caption := 'Option with no file selection';
  RadioButtons[0].OnClick := @RadioButtonClick;

  RadioButtons[1] := TNewRadioButton.Create(InputPage);
  RadioButtons[1].Parent := InputPage.Surface;
  RadioButtons[1].Left := RadioButtons[0].Left;
  RadioButtons[1].Top := RadioButtons[0].Top + RadioButtons[0].Height + 2;
  RadioButtons[1].Width := InputPage.SurfaceWidth;
  RadioButtons[1].Checked := False;
  RadioButtons[1].Caption := 'Option with file selection';
  RadioButtons[1].OnClick := @RadioButtonClick;

  ShiftDirPageItem(InputPage, 0, RadioButtons[1].Top);
  SetDirPageItemEnabled(InputPage, 0, False);
end;