안녕하세요?
아래 코드를 참조하세요. 아마도 원하시는 상수가 windows.pas정의되어 있을겁니다.

if Application.MessageBox('두번째 버튼에 포커스가 가죠?', '테스트', 292)
= ID_YES then
begin

end;

# windows.pas에 정의된 상수를 뽑았습니다.

  MB_OK = $00000000;
  MB_OKCANCEL = $00000001;
  MB_ABORTRETRYIGNORE = $00000002;
  MB_YESNOCANCEL = $00000003;
  MB_YESNO = $00000004;
  MB_RETRYCANCEL = $00000005;

  MB_ICONHAND = $00000010;
  MB_ICONQUESTION = $00000020;
  MB_ICONEXCLAMATION = $00000030;
  MB_ICONASTERISK = $00000040;
  MB_USERICON = $00000080;
  MB_ICONWARNING                 = MB_ICONEXCLAMATION;
  MB_ICONERROR                   = MB_ICONHAND;
  MB_ICONINFORMATION             = MB_ICONASTERISK;
  MB_ICONSTOP                    = MB_ICONHAND;

  MB_DEFBUTTON1 = $00000000;
  MB_DEFBUTTON2 = $00000100;
  MB_DEFBUTTON3 = $00000200;
  MB_DEFBUTTON4 = $00000300;

  MB_APPLMODAL = $00000000;
  MB_SYSTEMMODAL = $00001000;
  MB_TASKMODAL = $00002000;
  MB_HELP = $00004000;                          { Help Button }

  MB_NOFOCUS = $00008000;
  MB_SETFOREGROUND = $00010000;
  MB_DEFAULT_DESKTOP_ONLY = $00020000;

  MB_TOPMOST = $00040000;
  MB_RIGHT = $00080000;
  MB_RTLREADING = $00100000;

  MB_SERVICE_NOTIFICATION = $00200000;
  MB_SERVICE_NOTIFICATION_NT3X = $00040000;

  MB_TYPEMASK = $0000000F;
  MB_ICONMASK = $000000F0;
  MB_DEFMASK = $00000F00;
  MB_MODEMASK = $00003000;
  MB_MISCMASK = $0000C000;