Private Sub Form1_Load(ByVal sender As System.Object,
                         ByVal e As System.EventArgs) Handles MyBase.Load

    HelpProvider1.HelpNamespace = Application.StartupPath & "\proga.chm"

HelpNavigator на HelpProvider1 = TopicId
HelpKeyword на HelpProvider1 = 1

  App.HelpFile = App.Path & "\" & "proga.chm" 'для всего приложения

HelpContextID=1 для Form1
HelpContextID=20 для Form2

HelpProvider1.HelpNamespace = IO.Path.Combine(Application.StartupPath, "proga.chm")

'Form1
  Private Sub Form1_HelpRequested(ByVal sender As Object,
   ByVal hlpevent As System.Windows.Forms.HelpEventArgs) Handles Me.HelpRequested
     Help.ShowHelp(Me, IO.Path.Combine(Application.StartupPath, "proga.chm"), HelpNavigator.TopicId, "1")
  End Sub

'Form2
  Private Sub Form2_HelpRequested(ByVal sender As Object,
   ByVal hlpevent As System.Windows.Forms.HelpEventArgs) Handles Me.HelpRequested
     Help.ShowHelp(Me, IO.Path.Combine(Application.StartupPath, "proga.chm"), HelpNavigator.TopicId, "5")
  End Sub

  'в первом вызове первый параметр 0 - родитель не назначается, чтобы не было OnTop поведения
  HTMLHelp 0, App.Path & "\" & "proga.chm", HH_DISPLAY_TOPIC, ByVal helpTopic
  'второй вызов - первый параметр handle родителя - чтоб определиться куда окно help будет слать сообщения
  'при этом поведение OnTop относительно Form1 уже не сработает
  hwndHelp = HTMLHelp(Form1.hwnd, App.Path & "\" & "proga.chm", _
   HH_GET_WIN_HANDLE, ByVal "ProgaHelp")

Help.ShowHelp(Nothing, 

'Form2
  Private Sub Form2_HelpRequested(ByVal sender As Object,

Help.ShowHelp(Nothing, 

  Private Sub Form1_HelpRequested(ByVal sender As Object,
   ByVal hlpevent As System.Windows.Forms.HelpEventArgs) Handles Me.HelpRequested
    Help.ShowHelp(New Control(), help_path, HelpNavigator.TopicId, "1")
  End Sub
  Private Sub ButtonHelp_Click(ByVal sender As System.Object,
                               ByVal e As System.EventArgs) Handles ButtonHelp.Click
    'если нужна своя кнопка Help
    Form1_HelpRequested(Me, New System.Windows.Forms.HelpEventArgs(Cursor.Position))
  End Sub

    Help.ShowHelp(New Control(), help_path, HelpNavigator.TopicId, "1")
    HTMLHelp(IntPtr.Zero, help_path, HH_HELP_CONTEXT, 1)

  Public Declare Function HTMLHelp Lib "hhctrl.ocx" Alias "HtmlHelpA" _
   (ByVal hwndCaller As IntPtr, ByVal pszFile As String, _
    ByVal uCommand As Integer, ByVal dwData As Integer) As IntPtr
  Public Declare Function HTMLHelp_str Lib "hhctrl.ocx" Alias "HtmlHelpA" _
   (ByVal hwndCaller As IntPtr, ByVal pszFile As String, _
    ByVal uCommand As Integer, ByVal dwData As String) As IntPtr

  Public Const HH_HELP_CONTEXT = &HF             '  display mapped numeric

  ' Notification codes
  Public Const HHN_FIRST = (0 - 860)
  Public Const HHN_NAVCOMPLETE = (HHN_FIRST - 0)
  Public Const HHN_TRACK = (HHN_FIRST - 1)
  Public Const HHN_WINDOW_CREATE = (HHN_FIRST - 2)
'==========================
'В главной форме Form1
  Private Sub Form1_HelpRequested(ByVal sender As Object,
   ByVal hlpevent As System.Windows.Forms.HelpEventArgs) Handles Me.HelpRequested
    HTMLHelp(IntPtr.Zero, help_path, HH_HELP_CONTEXT, 1)
    Dim hwndHelp As IntPtr = HTMLHelp_str(Me.Handle, help_path, _
     HH_GET_WIN_HANDLE, "ProgaHelp")
  End Sub

  Private Sub ButtonHelp_Click(ByVal sender As System.Object,
                               ByVal e As System.EventArgs) Handles ButtonHelp.Click
    Form1_HelpRequested(Me, New System.Windows.Forms.HelpEventArgs(Cursor.Position))
  End Sub

  Protected Overrides Sub WndProc(ByRef m As System.Windows.Forms.Message)

    Select Case m.Msg

      Case WM_NOTIFY
        Dim uNMHDR As NMHDR = CType(Marshal.PtrToStructure(m.LParam, GetType(NMHDR)), NMHDR)
        Select Case uNMHDR.code
          Case HHN_TRACK
            'Debug.WriteLine("HHN_TRACK")
            Dim tHDN As NMHEADER = _
             CType(Marshal.PtrToStructure(m.LParam, GetType(NMHEADER)), NMHEADER)
            If tHDN.iButton = 5 Then 'кнопка Show
              Debug.WriteLine("Show button clicked in help")
            End If
          Case Else
        End Select
      Case Else
    End Select

    ' Forward message to base WndProc.
    MyBase.WndProc(m)

  End Sub
'===================
В Form2 например:
Public Class Form2

  Private Sub Form2_HelpRequested(ByVal sender As Object,
   ByVal hlpevent As System.Windows.Forms.HelpEventArgs) Handles Me.HelpRequested
    HTMLHelp(IntPtr.Zero, help_path, HH_HELP_CONTEXT, 5)
    Dim hwndHelp As IntPtr = HTMLHelp_str(Form1.Handle, help_path, _
     HH_GET_WIN_HANDLE, "ProgaHelp") '!!!Но Notifications от help вешаются на Form1 все равно
  End Sub

rbBand.cyMinChild = crcToolbar.Bottom + 2 'по фактической высоте Toolbar

  Private Sub s_Help_CallBackWndProc(ByRef m As System.Windows.Forms.Message, ByRef Cancel As Boolean) _
   Handles s_Help.CallBackWndProc
      Case WM_NOTIFY
        Dim uNMHDR As NMHDR = CType(Marshal.PtrToStructure(m.LParam, GetType(NMHDR)), NMHDR)
        Select Case uNMHDR.code
          Case TBN_DROPDOWN
            Dim nmTB As NMTOOLBAR = _
             CType(Marshal.PtrToStructure(m.LParam, GetType(NMTOOLBAR)), NMTOOLBAR)
            If nmTB.iItem = 1001 Then 'кнопка Interface
              'только виста+темы, в остальных случаях нет кнопки
              Dim pt As POINTAPI
              pt.x = nmTB.rcButton.Left
              pt.y = nmTB.rcButton.Bottom
              ClientToScreen(nmTB.hdr.hwndFrom, pt)
              'Form1.Visible = True 'для проверки чего происходит
              TrackPopupMenu(Form1.menu_HelpStyle.Handle, 0,
               pt.x, pt.y, 0, Form1.Handle)
              Cancel = True
            End If

              TrackPopupMenu(Me.menu_HelpStyle.Handle, 0,
               pt.x, pt.y, 0, Me.Handle)

   SetPopup(pt.x, pt.y)
...
  ' This delegate enables asynchronous calls for setting
   Delegate Sub SetPopupCallback(ByVal [x] As Integer, ByVal [y] As Integer)

    Private Sub SetPopup(ByVal [x] As Integer, ByVal [y] As Integer)

        ' InvokeRequired required compares the thread ID of the
        ' calling thread to the thread ID of the creating thread.
        ' If these threads are different, it returns true.
        If Me.textBox1.InvokeRequired Then
            Dim d As New SetPopupCallback(AddressOf SetPopup)
            Me.Invoke(d, New Object() {[x], [y]})
        Else
            TrackPopupMenu(Me.menu_HelpStyle.Handle, 0,
               [x], [y], 0, Me.Handle)
        End If
    End Sub

   SetForegroundWindow(hDlg);

   // Display the menu
   TrackPopupMenu(   hSubMenu,

          Case TBN_DROPDOWN
...
              'FormHelper.Visible = True 'для проверки чего происходит
              FormHelper.Tag = CType(m.HWnd, IntPtr) 'hwnd хэлпа
              TrackPopupMenu(FormHelper.menu_HelpStyle.Handle, 0,
               pt.x, pt.y, 0, FormHelper.Handle)
              Cancel = True

...в форме FormHelper
  Public Sub New()
    InitializeComponent()
    For Each menu_item As MenuItem In menu_HelpStyle.MenuItems
      AddHandler menu_item.Click, AddressOf MenuItem_Click
    Next
...
  Private Sub MenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
    For Each menu_item As MenuItem In menu_HelpStyle.MenuItems
      menu_item.Checked = False
    Next
    CType(sender, MenuItem).Checked = True
    Select Case CType(sender, MenuItem).Text
      Case "&Communications"
        params.m_HelpStyle = "Communications"
      Case "&Media"
...

  Private Sub Form1_HelpRequested(ByVal sender As Object,
   ByVal hlpevent As System.Windows.Forms.HelpEventArgs) Handles Me.HelpRequested
    Help.ShowHelp(New Control(), help_path, HelpNavigator.TopicId, "1")
  End Sub
  Private Sub ButtonHelp_Click(ByVal sender As System.Object,
                               ByVal e As System.EventArgs) Handles ButtonHelp.Click
    'если нужна своя кнопка Help
    Form1_HelpRequested(Me, New System.Windows.Forms.HelpEventArgs(Cursor.Position))
  End Sub