Public Class Form1

  'Window Notifications
  Public Const WM_GETICON = &H7F

  Public Const ICON_SMALL = 0
  Public Const ICON_BIG = 1

  'значения надо присваивать до Form1_Load!!!
  Dim IconTAB As Icon = New Icon(Me.Icon, 32, 32) 'иконка для Висты 32х32 для Alt+Tab
  Dim IconTASK As Icon = New Icon(Me.Icon, 16, 16) 'иконка 16х16 для Taskbar(это если XP)

  Protected Overrides Sub WndProc(ByRef m As System.Windows.Forms.Message)
    'Debug.WriteLine(m.ToString())

    Select Case m.Msg
      Case WM_GETICON
        If m.WParam = New IntPtr(ICON_BIG) Then 'запрос правильной иконки для Alt-Tab на Висте
          m.Result = IconTAB.Handle
          Exit Sub
        ElseIf m.WParam = New IntPtr(ICON_SMALL) Then 'запрос правильной иконки для TaskBar
          m.Result = IconTASK.Handle
          Exit Sub
        End If
      Case Else
    End Select

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

End Class

  Private Sub frm1_Load(sender As Object, e As EventArgs) Handles Me.Load
    SetWindowLong(Me.Handle, GWL_EXSTYLE, GetWindowLong(Me.Handle, GWL_EXSTYLE) Or WS_EX_APPWINDOW)