type
  TOSVersion = (osUnknown, os95, os98, osME, osNT3, osNT4, os2K, osXP);

function GetOS: TOSVersion;
var
  OS: TOSVersionInfo;
begin
  ZeroMemory(@OS,SizeOf(OS));
  OS.dwOSVersionInfoSize := SizeOf(OS);
  GetVersionEx(OS);
  Result := osUnknown;
  if OS.dwPlatformId = VER_PLATFORM_WIN32_NT then
  begin
    case OS.dwMajorVersion of
      3: Result := osNT3;
      4: Result := osNT4;
      5:
      begin
        case OS.dwMinorVersion of
          0: Result:= os2K;
          1: Result:= osXP;
        end;
      end;
    end;
  end
  else if (OS.dwMajorVersion = 4) and (OS.dwMinorVersion = 0) then
    Result := os95
  else if (OS.dwMajorVersion = 4) and (OS.dwMinorVersion = 10) then
    Result := os98
  else if (OS.dwMajorVersion = 4) and (OS.dwMinorVersion = 90) then
    Result := osME
end;