String line = "";
 
 
 
            if (openFileDialog1.ShowDialog() == DialogResult.OK)
            {
                textBox1.Text = openFileDialog1.FileName;
 
 
 
                ArrayList arr = new ArrayList(); 
 
                try
                {
                    // Create an instance of StreamReader to read from a file.
                    // The using statement also closes the StreamReader.
                    using (StreamReader sr = new StreamReader(openFileDialog1.FileName))
                    {
                        // Read and display lines from the file until the end of 
                        // the file is reached.
                        while ((line = sr.ReadLine()) != null)
                        {
 
                            foreach (string s in line.Split(new char []{'\t'})) 
                            {
                                string ss = s;
                                ss += "\n";
                                arr.Add(ss);
 
                            } //Console.WriteLine(line);
                        } 
                    }
                }
                catch (Exception ex)
                {
                    // Let the user know what went wrong.
                    MessageBox.Show(ex.Message);
                }
 
 
                //  MessageBox.Show(line);
 
 
                string str = "";
 
                for (int i = 0; i < arr.Count; i++)
                {
                    //using (sw)
                    //{
                    str += arr[i].ToString();
                    //}
                }
                MessageBox.Show(str);
 
                using (StreamWriter sw = new StreamWriter("TestFile.txt"))
                { sw.WriteLine("ghv");
                sw.Write("g");
                sw.WriteLine("ghv");
            }
            }

string b = a.Replace('\t','\n');

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            string line = "ammar\thassan\nshah\tnaqvi";
            ArrayList arr = new ArrayList(); 
            foreach (string s in line.Split(new char[] { '\t' })) 
            { 
                arr.Add(s + "\n"); 
            } 
            Console.WriteLine(line);
            string str = "";                 
            for (int i = 0; i < arr.Count; i++)                
            {                                      
                str += arr[i].ToString();                                  
            }
            Console.WriteLine(str);
            Console.ReadKey();
        }
    }
}

            string a = System.IO.File.ReadAllText(@"c:\csnet\a1.txt");
            string b = a.Replace('\t','\n');
            System.IO.File.WriteAllText(@"c:\csnet\a2.txt",b);