var rootEntry = new DirectoryEntry("WinNT:");

// Здесь узнать количество элементов в  rootEntry.Children ???


foreach (DirectoryEntry child in rootEntry.Children)
{
        DomainEntries.Add(new _DomainEntry(child.Name, child));
}

public static List<string> GetLocalGroupMember(string IP, string admin)
        {
            List<string> ResultList = new List<string>();
            using (DirectoryEntry entry = new DirectoryEntry(string.Format(@"WinNT://{0}/{1}, group", IP, admin)))
            //Подключаемся
            {
                IEnumerable members = (IEnumerable)entry.Invoke("Members", null);
                // Вот тут можно проверить количество мемберов
                foreach (object member in members)
                {
                    using (DirectoryEntry memberEntry = new DirectoryEntry(member))
                    {
                        ResultList.Add(string.Format(@"{0}\{1}", memberEntry.Parent.Name, memberEntry.Name));
                    }
                }
            }