Pour ouvrir une fenêtre Access à la taille souhaitée:

Global Const SW_HIDE = 0
Global Const SW_SHOWNORMAL = 1
Global Const SW_SHOWMINIMIZED = 2
Global Const SW_SHOWMAXIMIZED = 3

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

Function fSetAccessWindow(nCmdShow As Long)
Dim loX  As Long
Dim loForm As Form
    On Error Resume Next
    Set loForm = Screen.ActiveForm
    If Err <> 0 Then 'no Activeform
      If nCmdShow = SW_HIDE Then
        MsgBox "Cannot hide Access unless a form is on screen"
      Else
        loX = apiShowWindow(hWndAccessApp, nCmdShow)
        Err.Clear
      End If
    Else
        If nCmdShow = SW_SHOWMINIMIZED And loForm.Modal = True Then
            MsgBox "Cannot minimize Access with " & (loForm.Caption + " ")   & "form on screen"
        ElseIf nCmdShow = SW_HIDE And loForm.PopUp <> True Then
            MsgBox "Cannot hide Access with " & (loForm.Caption + " ") & "form on screen"
        Else
            loX = apiShowWindow(hWndAccessApp, nCmdShow)
        End If
    End If
    fSetAccessWindow = (loX <> 0)
End Function

J'ai trouvé ça ici.