storing hex from text file into byte array

Try this (.NET 2.0 or later):

using System;
using System.IO;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
       string[] lines = File.ReadAllLines("myfile.txt"); // say
       List list = new List();     

       foreach(string line in lines)
       {
          string[] hexes = line.Split(' ');
          foreach (string hex in hexes)
          {
             list.Add(Convert.ToByte(hex, 16));
          }
       }

       byte[] bytes = list.ToArray();

       // check it worked

       Console.Write("{ ");

       for(int i = 0; i < bytes.Length; i++)
       {
           Console.Write("0x" + bytes[i].ToString("x2"));
           if (i < bytes.Length - 1) Console.Write(",");
       }

       Console.WriteLine(" }");

       Console.ReadKey();
    }
}