C#

private void treeview1_AfterSelect(object sender, TreeViewEventArgs e)
{
    TreeNode node = sender as TreeNode;
    if(node != null)
    {
    // Check node.Tag for whatever here.
    }
}

"If a man empties his purse into his head, no man can take it away from him, for an investment in knowledge pays the best interest." -- Joseph E. O'Donnell

Can't manage to P/Invoke that Win32 API in .NET? Why not do interop the wiki way!

/// <summary>
/// Checks for the existence of the Microsoft 2.0 Winsock Proxy Client
/// </summary>
/// <remarks>
/// Assumptions based on Win2K/NT client and
///     http://support.microsoft.com/default.aspx?scid=kb;en-us;218482&Product=prs
/// </remarks>
[RunInstaller(true)]
public class CustomAction : System.Configuration.Install.Installer
{
    /// <summary>
    /// Required designer variable.
    /// </summary>
    private System.ComponentModel.Container components = null;

    public CustomAction()
    {
        // This call is required by the Designer.
        InitializeComponent();

        // TODO: Add any initialization after the InitComponent call
    }

    #region Component Designer generated code
    /// <summary>
    /// Required method for Designer support - do not modify
    /// the contents of this method with the code editor.
    /// </summary>
    private void InitializeComponent()
    {
        components = new System.ComponentModel.Container();
    }
    #endregion

    /// <summary>
    /// Custom install for client
    ///   Verifies the Winsock Client is not present or at least inactive.
    ///   Installs the application.
    ///   Creates the application registry key.
    /// </summary>
    /// <param name="stateSaver"></param>
    public override void Install(System.Collections.IDictionary stateSaver)
    {


        string fn = Path.Combine(Environment.SystemDirectory,@"Wspcpl32.cpl");

        if ( File.Exists( fn ) )
        {
            StringBuilder msg = new StringBuilder();

            msg.Append("TCA Navigator Install has detected the presence of the WinSock Proxy Client.");
            msg.Append(System.Environment.NewLine);
            msg.Append(System.Environment.NewLine);
            msg.Append("It is necessary to reconfigure (via Control Panel) so that the client is not active.");
            msg.Append(System.Environment.NewLine);
            msg.Append("If you have already done so, click OK to continue with the install.");
            msg.Append(System.Environment.NewLine);
            msg.Append("Otherwise, hit Cancel, since continuing installation may make your system unstable.");
            msg.Append(System.Environment.NewLine);
            msg.Append(System.Environment.NewLine);
            msg.Append("We recommending requesting that this be removed from your RADIA install configuration.");

            if (MessageBox.Show(msg.ToString(), "Winsock Proxy Client detected",
                MessageBoxButtons.OKCancel,
                MessageBoxIcon.Stop,
                MessageBoxDefaultButton.Button2) == DialogResult.Cancel)
            {
                throw new InstallException("Installation cancelled by user action.");
            }
        }


        base.Install(stateSaver);

Create your Setup project within your solution.
Add another project that will ba a class library.
Create code similar to what I posted earlier.
Include output of that class library in your project file system.
Right-click the setup project and View...Custom Actions.
Add the project output for your custom installer at the point you want.
Compile everything.