' Add a new control to the inner PictureBox.
Private Sub mnuControlsAdd_Click()
Dim ctl As TextBox
Dim prev As TextBox

    ' Create the control.
    m_NumControls = m_NumControls + 1
    Set ctl = Controls.Add( _
        "VB.TextBox", _
        "Text" & Format$(m_NumControls), _
        picInner)

    ' Position the control.
    Set prev = Controls("Text" & Format$(m_NumControls - 1))
    ctl.Move prev.Left, _
        prev.Top + prev.Height + 30, _
        prev.Width, prev.Height
    ctl.Text = ctl.Name

    ' Size picInner to hold the control.
    picInner.Move 0, 0, _
        ctl.Left + ctl.Width + 120, _
        ctl.Top + ctl.Height + 120

    ' Display the control.
    ctl.Visible = True

    ' Rearrange the scroll bars.
    ArrangeScrollBars
End Sub

For details on making a scrolled window, see How To: Make a scrolled window.