[MarcoGG]

            string input = "006162636465666700000000";
            StringBuilder output = new StringBuilder("");
            for (int i = 0; i < input.Length-1; i+=2)
            {
                Int32 n = Convert.ToInt32(input.Substring(i, 2), 16);
                if (n != 0)
                {
                    char C = Convert.ToChar(n);
                    output.Append(C);
                }
            }
            MessageBox.Show(output.ToString());

Prova...