Private Declare Function GetSystemMenu Lib "user32" _
(ByVal hwnd As Long, ByVal bRevert As Long) As Long
Private Declare Function RemoveMenu Lib "user32" _
(ByVal hMenu As Long, ByVal nPosition As Long, ByVal wFlags As Long) As Long
 
Private Const MF_BYPOSITION = &H400&

Private Sub Form_Load()
Dim hMenu As Long
' Получаем описатель меню
hMenu = GetSystemMenu(hwnd, 0)
' Удаляем меню закрыть
RemoveMenu hMenu, 6, MF_BYPOSITION
' Удаляем разделитель
RemoveMenu hMenu, 5, MF_BYPOSITION
End Sub