Comparing files in a directory.

[TheDarklord]

I have some code which search for mp3 files and extracts that information for each file in each folder in a directory.

private void ShowFiles_Click(object sender, EventArgs e)
{

foreach (string foldername in Directory.GetDirectories(DirectoryName))
            {
                MP3Header mp3hdr = new MP3Header();
                string Mp3Filename;

               

                foreach (string filename in Directory.GetFiles(foldername))
                {
                    string extension = Path.GetExtension(filename);
                    FileInfo f = new FileInfo(filename);


                    if (extension == FileTypeExtension)
                    {
                        this.listBox1.Items.Add(filename);
                    }


                    if (f.Length <= thisFileLength)
                    {
                        this.listBox2.Items.Add(filename);

                    }

                    // Form1 tag = new Form1();

                    bool boolIsMP3 = mp3hdr.ReadMP3Information(filename);

                    this.listBoxFileName.Items.Add(mp3hdr.strFileName);
                    this.listBox3.Items.Add(mp3hdr.lngFileSize.ToString());
                    this.listBoxBitRate.Items.Add(mp3hdr.intBitRate.ToString());
                    this.listBoxFrequency.Items.Add(mp3hdr.intFrequency.ToString());
                    this.listBoxstrMode.Items.Add(mp3hdr.strMode);
                    this.listBoxstrLength.Items.Add(mp3hdr.strLengthFormatted);

                    Mp3Filename = filename;

                }

What would be the best way to extend this code so that it can compare files in one folder to a file in another folder, so for a duplicate finder?