Private Sub Splitter_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single)
    Screen.MousePointer =  7 
End Sub

Private Sub Splitter_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single)
Dim Min As Long
Dim Max As Long
Dim dY As Single
Dim Top As Single
Dim QTop As Single
Const Step =  100  'Задать больше, если тормозно двигается 

Min = 600
Max = Me.InsideHeight - 600

If Button = 1 Then
    If CLng(Y / Step) <> CLng(OY / Step) Then
        Top = Me.Splitter.Top + Y
        If Top > Min And Top < Max Then
            OY = Y
            Me.Painting = False
                'Тут двигаются контролы

            Me.Painting = True
        End If
    End If
End If
End Sub

Private Sub Splitter_MouseUp(Button As Integer, Shift As Integer, X As Single, Y As Single)
    Screen.MousePointer =  0 
End Sub