[MS-Access] pregunta complicada

Buena pregunta, probá con esto:

Private Declare Function ShowWindow Lib "user32" _
(ByVal hwnd As Long, ByVal nCmdShow As Long) As Long






Private Sub Form_Open(Cancel As Integer)
Call ShowWindow(hWndAccessApp, SW_HIDE)

DoCmd.OpenForm "frm_main", windowmode:=acDialog


End Sub

Private Sub Form_Unload(Cancel As Integer)
Dim lngret As Long
lngret = ShowWindow(hWndAccessApp, SW_MAXIMIZE)
End Sub