[nik1967]

Raf-9600, Johny777,

А так не проще?

Код:

[Setup]
AppName=My program
AppVerName=My program 1.5
DefaultDirName={pf}\My program

[Languages]
Name: rus; MessagesFile: compiler:Languages\Russian.isl

[Types]
Name: full; Description: Full installation; Flags: iscustom

[Components]
Name: Game; Description: Game_Component;
Name: Game\Lokal; Description: Game_Local_Component; Flags: exclusive; Types: full;
Name: Game\Full; Description: Game_Full_Component; Flags: exclusive; 

[Files]
Source: Game.exe; DestDir: {app};
Source: d2data.mpq; DestDir: {app};

[Registry]
Root: HKLM; Subkey: "SOFTWARE\Blizzard Entertainment"; Flags: uninsdeletekey
Root: HKLM; Subkey: "SOFTWARE\Blizzard Entertainment\Diablo II"; ValueName: "InstallPath"; ValueType: String; ValueData: "{app}\"; Flags: uninsdeletekey 

[_Code]
function NextButtonClick(CurPageID: Integer): Boolean;
var
  AppPath: String;
begin
  Result:= true;
  AppPath:= RemoveQuotes(ExpandConstant('{reg:HKLM\SOFTWARE\Blizzard Entertainment\Diablo II\,InstallPath|}'));
if (CurPageID = wpSelectComponents) and  IsComponentSelected('Game\Lokal') then
if not FileExists(AppPath + 'Game.exe') and not FileExists(AppPath + 'd2data.mpq') then
if MsgBoxEx(0, 'Не найдены Game.exe и d2data.mpq'+#13#10+'Установить Game_Full_Component?', 'Проблема', MB_YESNO or MB_ICONQUESTION, 0, 10) = IDYES then 
  WizardForm.ComponentsList.Checked[2]:= True  /// где 2 - индекс компонета - 3-й по списку (отсчёт от 0)
else
  WizardForm.ComponentsList.Checked[1]:= True; /// где 1 - индекс компонета - 2-й по списку (отсчёт от 0)
end;