'Constantes para SendMessage
Global Const WM_LBUTTONUP = &H202
Global Const WM_SYSCOMMAND = &H112
Global Const SC_MOVE = &HF010
Global Const MOUSE_MOVE = &HF012

#If Win32 Then
    Declare Function SendMessage Lib "User32" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, _
                        ByVal wParam As Long, lParam As Long) As Long
#Else
    Declare Function SendMessage Lib "User" (ByVal hWnd As Integer, ByVal wMsg As Integer, _
                        ByVal wParam As Integer, lParam As Any) As Long
#End If

'
'Este código se pondrá en el Control_MouseDown...
'
Dim lngRet As Long

'Simular que se mueve la ventana, pulsando en el Control
If Button = 1 Then
    'Envía un MouseUp al Control
    lngRet = SendMessage(Control.hWnd, WM_LBUTTONUP, 0, 0)
    'Envía la orden de mover el form
    lngRet = SendMessage(FormX.hWnd, WM_SYSCOMMAND, MOUSE_MOVE, 0)
End If