OP's.. Já consegui...
Private Declare Function SetWindowLong Lib "user32" _
Alias "SetWindowLongA" (ByVal hwnd As Long, ByVal _
nIndex As Long, ByVal dwNewLong As Long) As Long
Private Declare Function GetWindowLong Lib "user32" _
Alias "GetWindowLongA" (ByVal hwnd As Long, ByVal _
nIndex As Long) As Long
Const WS_MINIMIZEBOX = &H20000
Const WS_MAXIMIZEBOX = &H10000
Const GWL_STYLE = (-16)
Private Declare Function DeleteMenu Lib "user32" (ByVal hMenu As Long, ByVal nPosition As Long, ByVal wFlags As Long) As Long
Private Declare Function GetSystemMenu Lib "user32" (ByVal hwnd As Long, ByVal bRevert As Long) As Long
Private Const MF_BYPOSITION = &H400&
Private Sub MDIForm_Load()
Dim lWnd As Long
lWnd = GetWindowLong(Me.hwnd, GWL_STYLE)
lWnd = lWnd And Not (WS_MAXIMIZEBOX)
lWnd = SetWindowLong(Me.hwnd, GWL_STYLE, lWnd)
end sub
