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

function GetDomainName: AnsiString;
 type
  WKSTA_INFO_100 = record
    wki100_platform_id: Integer;
    wki100_computername: PWideChar;
    wki100_langroup: PWideChar;
    wki100_ver_major: Integer;
    wki100_ver_minor: Integer;
  end;

  WKSTA_USER_INFO_1 = record
    wkui1_username: PChar;
    wkui1_logon_domain: PChar;
    wkui1_logon_server: PChar;
    wkui1_oth_domains: PChar;
  end;
 type
  //Win9X ANSI prototypes from RADMIN32.DLL and RLOCAL32.DLL 

 TWin95_NetUserGetInfo = function(ServerName, UserName: PChar; Level: DWORD; var
    BfrPtr: Pointer): Integer;
  stdcall;
  TWin95_NetApiBufferFree = function(BufPtr: Pointer): Integer;
  stdcall;
  TWin95_NetWkstaUserGetInfo = function(Reserved: PChar; Level: Integer; var
    BufPtr: Pointer): Integer;
  stdcall;

  //WinNT UNICODE equivalents from NETAPI32.DLL 

 TWinNT_NetWkstaGetInfo = function(ServerName: PWideChar; level: Integer; var
    BufPtr: Pointer): Integer;
  stdcall;
  TWinNT_NetApiBufferFree = function(BufPtr: Pointer): Integer;
  stdcall;

  function IsWinNT: Boolean;
  var
    VersionInfo: TOSVersionInfo;
  begin
    VersionInfo.dwOSVersionInfoSize := SizeOf(TOSVersionInfo);
    Result := GetVersionEx(VersionInfo);
    if Result then
      Result := VersionInfo.dwPlatformID = VER_PLATFORM_WIN32_NT;
  end;
 var

  Win95_NetUserGetInfo: TWin95_NetUserGetInfo;
  Win95_NetWkstaUserGetInfo: TWin95_NetWkstaUserGetInfo;
  Win95_NetApiBufferFree: TWin95_NetApiBufferFree;

  WinNT_NetWkstaGetInfo: TWinNT_NetWkstaGetInfo;
  WinNT_NetApiBufferFree: TWinNT_NetApiBufferFree;

  WSNT: ^WKSTA_INFO_100;
  WS95: ^WKSTA_USER_INFO_1;

  EC: DWORD;
  hNETAPI: THandle;
 begin
  try

    Result := '';

    if IsWinNT then
    begin
      hNETAPI := LoadLibrary('NETAPI32.DLL');
      if hNETAPI <> 0 then
      begin @WinNT_NetWkstaGetInfo := GetProcAddress(hNETAPI, 'NetWkstaGetInfo');
          @WinNT_NetApiBufferFree  := GetProcAddress(hNETAPI, 'NetApiBufferFree');

        EC := WinNT_NetWkstaGetInfo(nil, 100, Pointer(WSNT));
        if EC = 0 then
        begin
          Result := WideCharToString(WSNT^.wki100_langroup);
          WinNT_NetApiBufferFree(Pointer(WSNT));
        end;
      end;
    end
    else
    begin
      hNETAPI := LoadLibrary('RADMIN32.DLL');
      if hNETAPI <> 0 then
      begin @Win95_NetApiBufferFree := GetProcAddress(hNETAPI, 'NetApiBufferFree');
          @Win95_NetUserGetInfo := GetProcAddress(hNETAPI, 'NetUserGetInfoA');

        EC := Win95_NetWkstaUserGetInfo(nil, 1, Pointer(WS95));
        if EC = 0 then
        begin
          Result := WS95^.wkui1_logon_domain;
          Win95_NetApiBufferFree(Pointer(WS95));
        end;
      end;
    end;

  finally
    if hNETAPI <> 0 then
      FreeLibrary(hNETAPI);
  end;
 end;

 procedure TForm1.Button1Click(Sender: TObject);
 begin
  ShowMessage(GetDomainName);
 end;