{$IFDEF CONDITIONALEXPRESSIONS}
  {$IF Defined(TOSVersionInfoEx)}
    {$DEFINE TOSVERSIONINFOEX_DEFINED}
  {$IFEND}
{$ENDIF}
{$IFNDEF TOSVERSIONINFOEX_DEFINED}

type
  POSVersionInfoEx = ^TOSVersionInfoEx;
  TOSVersionInfoEx = packed record
    dwOSVersionInfoSize: DWORD;
    dwMajorVersion : DWORD;
    dwMinorVersion : DWORD;
    dwBuildNumber : DWORD;
    dwPlatformId : DWORD;
    szCSDVersion : array [0..127] of AnsiChar;
    wServicePackMajor : Word;
    wServicePackMinor : Word;
    wSuiteMask : Word;
    wProductType : Byte;
    wReserved : Byte;
  end;

const
  VER_SERVER_NT = $80000000;
  {$EXTERNALSYM VER_SERVER_NT}
  VER_WORKSTATION_NT = $40000000;
  {$EXTERNALSYM VER_WORKSTATION_NT}
  VER_SUITE_SMALLBUSINESS = $00000001;
  {$EXTERNALSYM VER_SUITE_SMALLBUSINESS}
  VER_SUITE_ENTERPRISE = $00000002;
  {$EXTERNALSYM VER_SUITE_ENTERPRISE}
  VER_SUITE_BACKOFFICE = $00000004;
  {$EXTERNALSYM VER_SUITE_BACKOFFICE}
  VER_SUITE_COMMUNICATIONS = $00000008;
  {$EXTERNALSYM VER_SUITE_COMMUNICATIONS}
  VER_SUITE_TERMINAL = $00000010;
  {$EXTERNALSYM VER_SUITE_TERMINAL}
  VER_SUITE_SMALLBUSINESS_RESTRICTED = $00000020;
  {$EXTERNALSYM VER_SUITE_SMALLBUSINESS_RESTRICTED}
  VER_SUITE_EMBEDDEDNT = $00000040;
  {$EXTERNALSYM VER_SUITE_EMBEDDEDNT}
  VER_SUITE_DATACENTER = $00000080;
  {$EXTERNALSYM VER_SUITE_DATACENTER}
  VER_SUITE_SINGLEUSERTS = $00000100;
  {$EXTERNALSYM VER_SUITE_SINGLEUSERTS}
  VER_SUITE_PERSONAL = $00000200;
  {$EXTERNALSYM VER_SUITE_PERSONAL}
  VER_SUITE_BLADE = $00000400;
  {$EXTERNALSYM VER_SUITE_BLADE}
  VER_SUITE_EMBEDDED_RESTRICTED = $00000800;
  {$EXTERNALSYM VER_SUITE_EMBEDDED_RESTRICTED}
  VER_SUITE_SECURITY_APPLIANCE = $00001000;
  {$EXTERNALSYM VER_SUITE_SECURITY_APPLIANCE}

const
  VER_NT_WORKSTATION = $0000001;
  {$EXTERNALSYM VER_NT_WORKSTATION}
  VER_NT_DOMAIN_CONTROLLER = $0000002;
  {$EXTERNALSYM VER_NT_DOMAIN_CONTROLLER}
  VER_NT_SERVER = $0000003;
  {$EXTERNALSYM VER_NT_SERVER}

{$ENDIF}  // TOSVERSIONINFOEX_DEFINED


function GetOSVersionInfo(var Info: TOSVersionInfoEx): Boolean;
begin
  FillChar(Info, SizeOf(TOSVersionInfoEx), 0);
  Info.dwOSVersionInfoSize := SizeOf(TOSVersionInfoEx);
  Result := GetVersionEx(TOSVersionInfo(Addr(Info)^));
  if (not Result) then
  begin
    FillChar(Info, SizeOf(TOSVersionInfoEx), 0);
    Info.dwOSVersionInfoSize := SizeOf(TOSVersionInfoEx);
    Result := GetVersionEx(TOSVersionInfo(Addr(Info)^));
    if (not Result) then
      Info.dwOSVersionInfoSize := 0;
  end;
end;

function GetOSVersionText: string;
var
  Info: TOSVersionInfoEx;
  Key: HKEY;
begin
  Result := '';
  if (not GetOSVersionInfo(Info)) then
    Exit;
  case Info.dwPlatformId of
    { Win32s }
    VER_PLATFORM_WIN32s:
      Result := 'Microsoft Win32s';
    { Windows 9x }
    VER_PLATFORM_WIN32_WINDOWS:
      if (Info.dwMajorVersion = 4) and (Info.dwMinorVersion = 0) then
      begin
        Result := 'Microsoft Windows 95';
        if (Info.szCSDVersion[1] in ['B', 'C']) then
          Result := Result +' OSR2';
      end
      else if (Info.dwMajorVersion = 4) and (Info.dwMinorVersion = 10) then
      begin
        Result := 'Microsoft Windows 98';
        if (Info.szCSDVersion[1] = 'A') then
          Result := Result + ' SE';
      end
      else if (Info.dwMajorVersion = 4) and (Info.dwMinorVersion = 90) then
        Result := 'Microsoft Windows Millennium Edition';
    { Windows NT }
    VER_PLATFORM_WIN32_NT:
      begin
        { Version }
        if (Info.dwMajorVersion = 5) and (Info.dwMinorVersion = 2) then
          Result := 'Microsoft Windows Server 2003'
        else if (Info.dwMajorVersion = 5) and (Info.dwMinorVersion = 1) then
          Result := 'Microsoft Windows XP'
        else if (Info.dwMajorVersion = 5) and (Info.dwMinorVersion = 0) then
          Result := 'Microsoft Windows 2000'
        else
          Result := 'Microsoft Windows NT';
        { Extended }
        if (Info.dwOSVersionInfoSize >= SizeOf(TOSVersionInfoEx)) then
        begin
          { ProductType }
          if (Info.wProductType = VER_NT_WORKSTATION) then
          begin
            if (Info.dwMajorVersion = 4) then
              Result := Result + #10'Workstation 4.0'
            else if(Info.wSuiteMask and VER_SUITE_PERSONAL <> 0) then
              Result := Result + #10'Home Edition'
            else
              Result := Result + #10'Professional';
          end
          else if (Info.wProductType = VER_NT_SERVER) then
          begin
             if (Info.dwMajorVersion = 5) and (Info.dwMinorVersion = 2) then
             begin
               if (Info.wSuiteMask and VER_SUITE_DATACENTER <> 0) then
                 Result := Result + #10'Datacenter Edition'
               else if (Info.wSuiteMask and VER_SUITE_ENTERPRISE <> 0) then
                 Result := Result + #10'Enterprise Edition'
               else if (Info.wSuiteMask = VER_SUITE_BLADE) then
                 Result := Result + #10'Web Edition'
               else
                 Result := Result + #10'Standard Edition';
             end
             else if (Info.dwMajorVersion = 5) and (Info.dwMinorVersion = 0) then
             begin
               if (Info.wSuiteMask and VER_SUITE_DATACENTER <> 0) then
                  Result := Result + #10'Datacenter Server'
               else if (Info.wSuiteMask and VER_SUITE_ENTERPRISE <> 0) then
                  Result := Result + #10'Advanced Server'
               else
                  Result := Result + #10'Server';
             end
             else
             begin
               Result := Result + #10'Server ' +
                 IntToStr(Info.dwMajorVersion) + '.' +
                 IntToStr(Info.dwMinorVersion);
               if (Info.wSuiteMask and VER_SUITE_ENTERPRISE <> 0) then
                 Result := Result + ', Enterprise Edition';
             end;
          end;
        end;
        { CSDVersion }
        if (Info.dwMajorVersion = 4) and
          (StrIComp(Info.szCSDVersion, 'Service Pack 6') = 0) and
          (RegOpenKeyEx(HKEY_LOCAL_MACHINE,
            'SOFTWARE\Microsoft\Windows NT\CurrentVersion\Hotfix\Q246009', 0,
            KEY_QUERY_VALUE, Key) = ERROR_SUCCESS) then
        begin
          Result := Result + #10'Service Pack 6a';
          RegCloseKey(Key);
        end
        else
          Result := Result + #10 + StrPas(Info.szCSDVersion);
        Result := Result + #10'(Build ' +
          IntToStr(Info.dwBuildNumber and $FFFF) + ')';
      end;
  end;
end;

////////////////////////////////////////////////////////////////////////////////

procedure TForm1.Button1Click(Sender: TObject);
begin
  ShowMessage(StringReplace(GetOSVersionText, #10, ' ', [rfReplaceAll]));
end;