Estimado YACosta
Usa el siguiente código
Option Explicit
Private Const WS_CLOSEBOX As Long = &H80000
Private Const WS_MAXIMIZEBOX As Long = &H10000
Private Const WS_MINIMIZEBOX As Long = &H20000
Private Const GWL_STYLE As Long = (-16)
Private Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA" (ByVal hWnd As Long, ByVal nIndex As Long) As Long
Private Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hWnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
Private Sub Command1_Click()
MDIForm1.Caption = "Ventana Form1"
Form1.Show
YAcostaStyleForm MDIForm1.hWnd
End Sub
Private Sub MDIForm_Initialize()
YAcostaStyleForm Me.hWnd
End Sub
Private Sub YAcostaStyleForm(ByVal hWnd As Long)
Dim lWnd As Long
lWnd = GetWindowLong(hWnd, GWL_STYLE)
lWnd = lWnd And Not (WS_MINIMIZEBOX)
lWnd = lWnd And Not (WS_MAXIMIZEBOX)
lWnd = lWnd And Not (WS_CLOSEBOX)
lWnd = SetWindowLong(hWnd, GWL_STYLE, lWnd)
End Sub
Saludos, desde algún lugar de Lima-Perú