// Эта процедура перечисляет все возможные режимы на твоём компутере...
procedure TForm1.FormCreate(Sender: TObject);
Var
  PDevMode: ^_DEVICEMODEA;
  J: Integer;
begin
  New(PDevMode);
  ZeroMemory(PDevMode, SizeOf(PDevMode^));
  J := 0;
  PDevMode.dmSize := SizeOf(PDevMode^);
  LBox.Clear;
  While EnumDisplaySettings(Nil, J, PDevMode^) Do
  Begin
    LBox.Items.AddObject(Format('%d BPP, %d x %d, %d Hz', [PDevMode.dmBitsPerPel, PDevMode.dmPelsWidth, PDevMode.dmPelsHeight, PDevMode.dmDisplayFrequency]), TObject(PDevMode));
    New(PDevMode);
    ZeroMemory(PDevMode, SizeOf(PDevMode^));
    PDevMode.dmSize := SizeOf(PDevMode^);
    Inc(J);
  End;
end;

//А эта процедура выставляет нужный режим
procedure TForm1.Button2Click(Sender: TObject);
Type PDevMode = ^_DEVICEMODEA;
Var aDevMode: _DEVICEMODEA;
begin
  If LBox.ItemIndex = -1 Then Exit;
  aDevMode := PDevMode(LBox.Items.Objects[LBox.ItemIndex])^;
  aDevMode.dmFields := DM_BITSPERPEL + DM_PELSWIDTH + DM_PELSHEIGHT;
  Case ChangeDisplaySettings(aDevMode, 0) Of
    DISP_CHANGE_RESTART: Raise Exception.Create('The computer must be restarted in order for the graphics mode to work.');
    DISP_CHANGE_BADFLAGS: Raise Exception.Create('An invalid set of flags was passed in.');
    DISP_CHANGE_FAILED: Raise Exception.Create('The display driver failed the specified graphics mode.');
    DISP_CHANGE_BADMODE: Raise Exception.Create('The graphics mode is not supported.');
    DISP_CHANGE_NOTUPDATED: Raise Exception.Create('Windows NT only: Unable to write settings to the registry.');
  End;
end;