using System;
using System.Windows.Forms;
using System.Runtime.InteropServices;

public partial class MainForm : Form
{
    public MainForm()
    {
        this.Menu = new MainMenu(new MenuItem[] {
			  	 new MenuItem("Trace", new EventHandler(Trace)),
			});
    }

    private void Trace(object sender, EventArgs e)
    {
        IChildFormProxy cfa = new ChildFormProxy();
        cfa.SetParent(this.Handle);
    }
}

public interface IChildFormProxy
{
    void SetParent(IntPtr hwnd);
}

public class Win32Window : IWin32Window
{
    public Win32Window(IntPtr hwnd)
    {
        _Handle = hwnd;
    }
    public IntPtr Handle
    {
        get { return _Handle; }
    }
    private IntPtr _Handle;
}

public class ChildFormProxy : IChildFormProxy
{
    public void SetParent(IntPtr hwnd)
    {
        ChildForm cf = new ChildForm(hwnd);
        cf.Show();
    }
}

public class ChildForm : Form
{
    public ChildForm(IntPtr parentHwnd)
    {
        this.FormBorderStyle = FormBorderStyle.FixedSingle;
        this.ControlBox = false;
        this.TopLevel = false;
        this.BackColor = System.Drawing.Color.Red;
        _ParentHwnd = parentHwnd;
    }
    private IntPtr _ParentHwnd;

    protected override CreateParams CreateParams
    {
        get
        {
            CreateParams cp = base.CreateParams;
            cp.Parent = _ParentHwnd;
            return cp;
        }
    }
}