Public Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hWnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long

Public Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (Destination As Any, Source As Any, ByVal Length As Long)

Public Declare Function CallWindowProc Lib "user32" Alias "CallWindowProcA" (ByVal lpPrevWndFunc As Long, ByVal hWnd As Long, ByVal Msg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long

Public Const WM_GETMINMAXINFO = &H24

Public Type POINTAPI
        x As Long
        y As Long
End Type

Public Const GWL_WNDPROC = (- 4 )

Public Type MINMAXINFO
        ptReserved As POINTAPI
        ptMaxSize As POINTAPI
        ptMaxPosition As POINTAPI
        ptMinTrackSize As POINTAPI
        ptMaxTrackSize As POINTAPI
End Type

Global MMI As MINMAXINFO

Global Prev_hWnd As Long
Function WinAPI_GMMI(ByVal hWnd As Long, ByVal Msg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
If Msg = WM_GETMINMAXINFO Then
    Call CopyMemory(MMI, lParam, Len(MMI))
    MMI.ptMinTrackSize.y =  100 
    MMI.ptMinTrackSize.x =  100 
Else
    WinAPI_GMMI = CallWindowProc(Prev_hWnd, hWnd, Msg, wParam, lParam)
End If
End Function
Sub SubClass()
Prev_hWnd = SetWindowLong(Form1.hWnd, GWL_WNDPROC, AddressOf WinAPI_GMMI)
End Sub
Sub UnSubClass()
Call SetWindowLong(Form1.hWnd, GWL_WNDPROC, Prev_hWnd)
End Sub