// Запись
Stream stream = new FileStream("data.bin");
foreach (FileStream fs in files.Select(path => new FileStream(path, FileMode.Open))) {
    fs.CopyTo(stream);
    fs.Close();
}

// Чтение
foreach (CFileHeader cFileHeader in header.FileHeaders) {
    FileStream fs = new FileStream("data/" + cFileHeader.Name, FileMode.Create);
    byte[] buffer = new byte[cFileHeader.Size];
    stream.Read(buffer, 0, buffer.Length);
    fs.Write(buffer, 0, buffer.Length);
    fs.Close();
}