Convert float to its binary representation (using MemoryStream?)

You can use BitConverter.GetBytes(float) or use a BinaryWriter wrapping a MemoryStream and use BinaryWriter.Write(float). It's not clear exactly what you did with a MemoryStream before, but you don't want to use StreamWriter - that's for text.

Using BitConverter, not MemoryStream:

        // -7 produces "1 10000001 11000000000000000000000"
        static string FloatToBinary(float f)
        {
            StringBuilder sb = new StringBuilder();
            Byte[] ba = BitConverter.GetBytes(f);
            foreach (Byte b in ba)
                for (int i = 0; i < 8; i++)
                {
                    sb.Insert(0,((b>>i) & 1) == 1 ? "1" : "0");
                }
            string s = sb.ToString();
            string r = s.Substring(0, 1) + " " + s.Substring(1, 8) + " " + s.Substring(9); //sign exponent mantissa
            return r;
        }