procedure RegisterTypeLibrary(const Is64Bit: Boolean; const Filename: String);

Registers the type library with the specified filename. If Is64Bit is True, the type library will be registered in a 64-bit process. Raises an exception if not successful.

begin
  // Register stdole2.tlb located in the System directory.
  RegisterTypeLibrary(Is64BitInstallMode, ExpandConstant('{sys}\stdole2.tlb'));
end;

Because we specify Is64BitInstallMode in the first parameter, it will register the 64-bit type library in the 64-bit System directory when Setup is running in 64-bit mode. Otherwise, it will register the 32-bit type library in the 32-bit System directory.