Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

{ 
  An application sends the WM_WININICHANGE message to all top-level windows 
  after making a change to the WIN.INI file. 
  The SystemParametersInfo function sends this message after an application uses the 
  function to change a setting in WIN.INI. 
}

 type
   TForm1 = class(TForm)
   private
    { Private declarations }
    procedure WMWinIniChange(var Message: TMessage); message WM_WININICHANGE;
    // or WM_SETTINGCHANGE 
  end;

 var
   Form1: TForm1;

 implementation

 {$R *.dfm}

 procedure TForm1.WMWinIniChange(var Message: TMessage);
 var
   status: Bool;
   Area: TRect;
 begin
   inherited;
   case Message.wParam of
       // Example: Detect when the screen saver is enabled/disabled 
      SPI_SETSCREENSAVEACTIVE:
       begin
         SystemParametersInfo(SPI_GETSCREENSAVEACTIVE, 0, @status, 0);
         if Status = True then
           ShowMessage('Screensaver has been enabled.')
         else
           ShowMessage('Screensaver has been disabled.');
       end;
   end;
 end;