private void PopulateLibrary()
{
    TreeNode artist;
    TreeNode album;
    TreeNode song;
    //objects to get artists
    DirectoryInfo dir = new DirectoryInfo(ROOTDIR);
    //objects to get the albums
    DirectoryInfo[] subDirs = dir.GetDirectories();
    //get the songs
    FileInfo[] files = dir.GetFiles();
    // Add all the sub-directories
    foreach (DirectoryInfo dirInfo in dir.GetDirectories("*.*"))
    {
        // Add the artist node
        artist = new TreeNode(dirInfo.FullName.Substring(dirInfo.FullName.LastIndexOf(Path.DirectorySeparatorChar) + 1));
        foreach (DirectoryInfo sd in subDirs)
        {
            album = new TreeNode(sd.Name);
            artist.ChildNodes.Add(album);
            for (int i = 0; i < subDirs.Length; i++)
            {
                foreach (FileInfo fi in files)
                {
                    song = new TreeNode(fi.Name);
                    album.ChildNodes.Add(song);
                }
            }
        }
        // Add the nodes
        MediaLibrary.Nodes.Add(artist);
        MediaLibrary.CollapseAll();
    }
}

private void PopulateLibrary() {
    PopulateLibrary(new DirectoryInfo(ROOTDIR));
}

// assumes, rootDir/artistDir/albumDir/songFile
private void PopulateLibrary(DirectoryInfo rootDir) {
    foreach (DirectoryInfo artistDir in rootDir.GetDirectories()) {
        TreeNode artistNode = new TreeNode( artistDir.Name );
        foreach (DirectoryInfo albumDir in artistDir.GetDirectories()) {
            TreeNode albumNode = new TreeNode(albumDir.Name);
            foreach (FileInfo songFile in albumDir.GetFiles()) {
                albumNode.ChildNodes.Add( new TreeNode(songFile.Name) );
            }
            artistNode.ChildNodes.Add(albumNode);
        }
        // Add the nodes
        MediaLibrary.Nodes.Add(artistNode);
    }
    MediaLibrary.CollapseAll();
}

const string ROOTDIR = @"C:\Documents and Settings\<Name Removed>\My Documents\My Music\";

const string ROOTDIR = @"C:\Documents and Settings\Jason\My Documents\";

this.MediaLibrary.SelectedValue

<!-- Media Player for IE -->
<object id="Player1" width="320" height="240"
    classid="clsid:6BF52A52-394A-11d3-B153-00C04F79FAA6"    
    type="application/x-ms-wmp">
    <param name="URL" value=""/>
</object>

<!-- Media Player for FF -->
<object id="Player2" width="320" height="240"
    type="application/x-ms-wmp">
    <param name="URL" value=""/>

private void LoadSong(string song)
{
    HttpContext.Current.Response.Write(song);
    Player.Filename = song;
    Player.AutoStart = true;
}

protected void MediaLibrary_SelectedNodeChanged(object sender, EventArgs e)
{
    LoadSong(ROOTDIR + this.MediaLibrary.SelectedNode.Parent.Parent.Text.ToString() + "\\" +
    this.MediaLibrary.SelectedNode.Parent.Text.ToString() + "\\" + this.MediaLibrary.SelectedValue);
}