this methods are depricated from framework 2.0 but still we need way to do this...so this is the way...

public static uint IPAddressToLong(string IPAddr)
        {
            IPAddress oIP = IPAddress.Parse(IPAddr);
            byte[] byteIP = oIP.GetAddressBytes();


            uint ip = (uint)byteIP[0] << 24;
            ip += (uint)byteIP[1] << 16;
            ip += (uint)byteIP[2] << 8;
            ip += (uint)byteIP[3];

            return ip;
        }

        public static string LongToIPAddress(uint ipLong)
        {
            //string ipAddress = string.Empty;
            byte[] addByte = new byte[4];

            addByte[0] = (byte)((ipLong >> 24) & 0xFF);
            addByte[1] = (byte)((ipLong >> 16) & 0xFF);
            addByte[2] = (byte)((ipLong >> 8) & 0xFF);
            addByte[3] = (byte)((ipLong >> 0) & 0xFF);

            return addByte[0].ToString() + "." + addByte[1].ToString() + "." + addByte[2].ToString() + "." + addByte[3].ToString();
        }