Hola: Tenes que usar estas declaraciones de la API en un modulo de código
Public Const WM_SYSCOMMAND = &H112
Public Const SC_RESTORE = &HF120
Public Const SWP_NOMOVE = 2
Public Const SWP_NOSIZE = 1
Public Const SWP_HIDEWINDOW = &H80
Public Const SWP_SHOWWINDOW = &H40
Public Const FLAGS = SWP_NOMOVE Or SWP_NOSIZE
Public Const HWND_TOPMOST = -1
Public Const HWND_NOTOPMOST = -2
Public Const WM_SETREDRAW = &HB
' Llamadas al API de Windows para crear la ventana Topmost
Declare Function SetWindowPos Lib "User32" (ByVal h&, ByVal hb&, ByVal x&, ByVal y&, ByVal cx&, ByVal cy&, ByVal f&) As Long
Declare Function FindWindow Lib "User32" (ByVal lpClassName As Any, ByVal lpWindowName As Any) As Long
Declare Function SendMessage Lib "User32" (ByVal hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long
Luego la llamada es algo asi:
'Mostrar el formulario centrado
Dim lWS As Long, lHS As Long
lWS = Screen.Width \ 2 - form1.Width \ 2
lHS = Screen.Height \ 2 - form1.Height \ 2
form1.Left = lWS
form1.Top = lHS
lHandle = form1.hWnd
Success% = SetWindowPos(lHandle, HWND_TOPMOST, lWS, lHS, 0, 0, FLAGS Or SWP_SHOWWINDOW)
'ocultar el formulario
Success% = SetWindowPos(lHandle, HWND_NOTOPMOST, 0, 0, 0, 0, FLAGS Or SWP_HIDEWINDOW)
espero te sirva
saludos