Windows Service with input during onStart()

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Diagnostics;
using System.Linq;
using System.ServiceProcess;
using System.Text;

using System.IO;
using System.Threading;
using System.Net;
using System.Net.NetworkInformation;
using System.Net.Sockets;
using Microsoft.Win32;

namespace SampleService
{
    public partial class SampleWinService : ServiceBase
    {

        #region Variable and Constants

        private Timer service_timer;
        NetworkInterface[] fNetworkInterfaces = NetworkInterface.GetAllNetworkInterfaces();
        NetworkInterface adapter;
        long start_received_bytes;
        long start_sent_bytes;
        long end_received_bytes;
        long end_sent_bytes;

        string start_time, end_time;
        private DateTime _startTime = DateTime.MinValue;

        private bool _isNetworkOnline;
        bool flag_c;

        string empty_line = "===============================================================";
        string path_file = @"C:\\Documents and Settings\\users\\Desktop\\Test Services.txt";

        #endregion

        // How do I input the file path, as it differs from system to system

        public SampleWinService()
        {
            InitializeComponent();                 
        }

        protected void timerTicker(object sender)
        {
            if (IsConnectedToInternet() == true && flag_c == false)
            {
                mark_values("initial");
                flag_c = true;
            }
            else if (IsConnectedToInternet() == true && flag_c == true)
            {
                mark_values("final");
            }
            else if (IsConnectedToInternet() == false && flag_c == true)
            {
                writetoFile();
                flag_c = false;
            }
        }

        protected void mark_values(string todo)
        {
            if (todo == "initial")
            {
                _startTime = DateTime.Now;
                start_received_bytes = adapter.GetIPv4Statistics().BytesReceived;
                start_sent_bytes = adapter.GetIPv4Statistics().BytesSent;
            }
            else
            {
                end_received_bytes = adapter.GetIPv4Statistics().BytesReceived;
                end_sent_bytes = adapter.GetIPv4Statistics().BytesSent;
            }
        }

        protected long cal_bytes(long value)
        {
            long temp_val;
            temp_val = (value / 1048576 * 100000) / 100000;
            return temp_val;
        }

        protected void writetoFile()
        {
            var timeSinceStartTime = DateTime.Now - _startTime;
            timeSinceStartTime = new TimeSpan(timeSinceStartTime.Hours,
                                              timeSinceStartTime.Minutes,
                                              timeSinceStartTime.Seconds);

            if (System.IO.File.Exists(path_file))
            {
                System.IO.File.AppendAllText(path_file, 
                    empty_line + Environment.NewLine + 
                    "Connection established: " + start_time + " Ended: " + end_time + Environment.NewLine +
                    "Total Time: " + timeSinceStartTime + Environment.NewLine +
                    "Received Start: " + start_received_bytes.ToString() + " (in MB): " + cal_bytes(start_received_bytes).ToString() + Environment.NewLine +
                    "Sent Start: " + start_sent_bytes.ToString() + " (in MB): " + cal_bytes(start_sent_bytes).ToString() + Environment.NewLine + 
                    "Received End: " + end_received_bytes.ToString() + " (in MB): " + cal_bytes(end_received_bytes).ToString() + Environment.NewLine + 
                    "Sent End: " + end_sent_bytes.ToString() + " (in MB): " + cal_bytes(end_sent_bytes).ToString() + Environment.NewLine);
            }
        }

        #region Internet Connection Status

        [System.Runtime.InteropServices.DllImport("wininet.dll")]
        private extern static bool InternetGetConnectedState(out int Description, int ReservedValue);
        public static bool IsConnectedToInternet()
        {
            int Desc;
            return InternetGetConnectedState(out Desc, 0);
        }

        protected void NetworkChange_NetworkAvailabilityChanged(object sender, System.Net.NetworkInformation.NetworkAvailabilityEventArgs e)
        {
            _isNetworkOnline = e.IsAvailable;
        }

        #endregion

        protected override void OnStart(string[] args)
        {
            try
            {
                // how do I assign the adpter dynamicaly or atleast during the installation of the services
                    adapter = fNetworkInterfaces[0];
                
                service_timer = new Timer(new TimerCallback(timerTicker));
                service_timer.Change(29999, 30000);                  
            }
            catch (Exception ex)
            {
                Console.WriteLine(" Start Error: {0}", ex.Message.ToString());
            }
        }

        protected override void OnStop()
        {
            
        }

    }
}