The following is how to use ToolStripPanels correctly in an MDIParent. This is important, because due to layering and MDI limiations, use of ToolStripContainer doesn't work well.

  public Form1()
  {
   // Make Form MDI Parent
   this.IsMdiContainer = true;

   // Add toolstrip panels
   ToolStripPanel tspTop = new ToolStripPanel();
   ToolStripPanel tspBottom = new ToolStripPanel();
   ToolStripPanel tspLeft = new ToolStripPanel();
   ToolStripPanel tspRight = new ToolStripPanel();

   // dock the ToolStripPanels
   tspTop.Dock = DockStyle.Top;
   tspBottom.Dock = DockStyle.Bottom;
   tspLeft.Dock = DockStyle.Left;
   tspRight.Dock = DockStyle.Right;

   // add toolstrips to move around between the panels
   ToolStrip tsTop = new ToolStrip();
   tsTop.Items.Add("Top");
   tspTop.Join(tsTop);

   ToolStrip tsBottom = new ToolStrip();
   tsBottom.Items.Add("Bottom");
   tspBottom.Join(tsBottom);

   ToolStrip tsRight = new ToolStrip();
   tsRight.Items.Add("Right");
   tspRight.Join(tsRight);

   ToolStrip tsLeft = new ToolStrip();
   tsLeft.Items.Add("Left");
   tspLeft.Join(tsLeft);

   // add menustrip, with new window
   MenuStrip ms = new MenuStrip();
   ToolStripMenuItem windowMenu = new ToolStripMenuItem("Window");
   ToolStripMenuItem windowNewMenu = new ToolStripMenuItem("New", null, new EventHandler(windowNewMenu_Click));
   windowMenu.DropDownItems.Add(windowNewMenu);
   ((ToolStripDropDownMenu)(windowMenu.DropDown)).ShowImageMargin = false;
   ((ToolStripDropDownMenu)(windowMenu.DropDown)).ShowCheckMargin = true;

   ms.MdiWindowListItem = windowMenu;

   ms.Items.Add(windowMenu);
   ms.Dock = DockStyle.Top;

   // Form.MainMenuStrip determines merge target
   MainMenuStrip = ms;

   // add a button to the MDIClient area
   Button b = new Button();
   b.AutoSize = true;
   b.Text = "In the MDI Container";

   // Add the ToolStripPanels to the form in reverse order
   this.Controls.Add(tspRight);
   this.Controls.Add(tspLeft);
   this.Controls.Add(tspBottom);
   this.Controls.Add(tspTop);

   // add menustrip last - Z order!
   this.Controls.Add(ms);

  }

  void windowNewMenu_Click(object sender, EventArgs e)
  {
   Form f = new Form();
   f.MdiParent = this;
   f.Text = "Form - " + this.MdiChildren.Length.ToString();
   f.Show();

  }
 }