Private Declare Function SetWindowPos Lib "user32" (ByVal hwnd As Long, ByVal hWndInsertAfter As Long, ByVal x As Long, ByVal y As Long, ByVal cx As Long, ByVal cy As Long, ByVal wFlags As Long) As Long
Const SWP_NOSIZE = &H1
Const SWP_NOMOVE = &H2
Const SWP_NOZORDER = &H4
Const SWP_NOREDRAW = &H8
Const SWP_NOACTIVATE = &H10
Const SWP_FRAMECHANGED = &H20        '  The frame changed: send WM_NCCALCSIZE
Const SWP_SHOWWINDOW = &H40
Const SWP_HIDEWINDOW = &H80
Const SWP_NOCOPYBITS = &H100
Const SWP_NOOWNERZORDER = &H200      '  Don't do owner Z ordering
Const SWP_DRAWFRAME = SWP_FRAMECHANGED
Const SWP_NOREPOSITION = SWP_NOOWNERZORDER
' SetWindowPos() hwndInsertAfter values
Const HWND_TOP = 0
Const HWND_BOTTOM = 1
Const HWND_TOPMOST = -1
Const HWND_NOTOPMOST = -2
Private Sub Command1_Click() 'Поверх всех окон
    Dim i
    i = SetWindowPos(hwnd, HWND_TOPMOST, 0, 0, 0, 0, SWP_NOSIZE Or SWP_NOMOVE)
End Sub
Private Sub Command2_Click() 'Не поверх всех окон
    Dim i
    i = SetWindowPos(hwnd, HWND_NOTOPMOST, 0, 0, 0, 0, SWP_NOSIZE Or SWP_NOMOVE)
End Sub
или проше:
Private Declare Function SetWindowPos Lib "user32" (ByVal hwnd As Long, ByVal hWndInsertAfter As Long, ByVal x As Long, ByVal y As Long, ByVal cx As Long, ByVal cy As Long, ByVal wFlags As Long) As Long
Const SWP_NOSIZE = &H1
Const SWP_NOMOVE = &H2
Const HWND_TOPMOST = -1
Private Sub Form_Load()
Dim i
i = SetWindowPos(hwnd, HWND_TOPMOST, 0, 0, 0, 0, SWP_NOSIZE Or SWP_NOMOVE)
End Sub