Esto lo penes en FormLoad:
hMenu = GetSystemMenu(Me.hwnd, 0)
If hMenu Then
'Obtenemos el número de elementos del menú
menuItemCount = GetMenuItemCount(hMenu)
'último es menuItemCount - 1
Call RemoveMenu(hMenu, menuItemCount - 1, MF_REMOVE Or MF_BYPOSITION)
Call RemoveMenu(hMenu, menuItemCount - 2, MF_REMOVE Or MF_BYPOSITION)
Call DrawMenuBar(Me.hwnd)
End If
y esto en un modulo:
Public Const MF_BYPOSITION = &H400
Public Const MF_REMOVE = &H1000
Public Declare Function DrawMenuBar Lib "user32" (ByVal hwnd As Long) As Long
Public Declare Function GetMenuItemCount Lib "user32" (ByVal hMenu As Long) As Long
Public Declare Function GetSystemMenu Lib "user32" (ByVal hwnd As Long, ByVal bRevert As Long) As Long
Public Declare Function RemoveMenu Lib "user32" (ByVal hMenu As Long, ByVal nPosition As Long, ByVal wFlags As Long) As Long
Y listo ya deshabilitaste el botn cerrar de un formulario o de vario siempre y cuado pogas lo primero en formload.
:-)