Converting a binairy to decimal is easy:

long l = Convert.ToInt64(txtMBBS.Text, 2);

int i = (int)l;

converting a decimal to a binairy can be a litlle bit harder:

public static string ToBinary(Int64 Decimal)

        {

            // Declare a few variables we're going to need

            Int64 BinaryHolder;

            char[] BinaryArray;

            string BinaryResult = "";

            while (Decimal > 0)

            {

                BinaryHolder = Decimal % 2;

                BinaryResult += BinaryHolder;

                Decimal = Decimal / 2;

            }

             // The algoritm gives us the binary number in reverse order (mirrored)

            // We store it in an array so that we can reverse it back to normal

            BinaryArray = BinaryResult.ToCharArray();

            Array.Reverse(BinaryArray);

            BinaryResult = new string(BinaryArray);

            return BinaryResult;

        }

Found this function on this site: http://kyrathaba.dcmembers.com/errata/binary_decimal.htm