{$IFNDEF WIN32}
           const WF_WINNT = $4000;
         {$ENDIF}

         function IsNT : bool;
         {$IFDEF WIN32}
          var
            osv : TOSVERSIONINFO;
         {$ENDIF}
         begin
           result := true;
          {$IFDEF WIN32}
           GetVersionEx(osv);
           if osv.dwPlatformId = VER_PLATFORM_WIN32_NT then exit;
          {$ELSE}
            if ((GetWinFlags and WF_WINNT) = WF_WINNT ) then exit;
          {$ENDIF}
           result := false;
         end;

       procedure TForm1.Button1Click(Sender: TObject);
       begin
         if IsNt then
           ShowMessage('Running on NT/Corriendo bajo NT')
         else
           ShowMessage('Not Running on NT/No corriendo bajo NT');
       end;