string fileName = "testing.txt";
string path = System.Windows.Forms.Application.StartupPath + @"\" + fileName;
FileStream txtFile = new FileStream(path, FileMode.Append);
StreamWriter writer = new StreamWriter(txtFile);
writer.WriteLine("[autorun]");
writer.WriteLine("icon=");
fileName = System.IO.Path.ChangeExtension(path,".inf");
writer.Close();
txtFile.Close();