[roman]

Otra forma:

function IsValidIP(S: String): Boolean;
var
  Strings: TStringList;

begin
  Result := false;

  Strings := TStringList.Create;
  Strings.Delimiter := '.';
  Strings.DelimitedText := S;

  if Strings.Count <> 4 then exit;

  repeat
    Result := (StrToIntDef(Strings[0], -1) in [0..255]);
    Strings.Delete(0);
  until (Strings.Count = 0) or not Result;

  Strings.Free;
end;

// Saludos