uses
  Registry;

function InstallScreenSaver(const AFileName: string): Boolean;
var
  Registry: TRegistry;
const
  ScreenSaverKey = 'Control Panel\Desktop';
begin
  Result := False;
  Registry := TRegistry.Create;
  try
    Registry.RootKey := HKEY_CURRENT_USER;
    if Registry.OpenKey(ScreenSaverKey, False) then
    begin
      Registry.WriteString('SCRNSAVE.EXE', AFileName);
      Result := True;
    end;
  finally
    Registry.Free;
  end;
end;