Aggiungi al form il seguente codice:
codice:
    Protected Overrides Sub WndProc(ByRef m As System.Windows.Forms.Message)
        Const WM_NCHITTEST As Integer = &H84
        Const HTCLIENT As Integer = 1
        Const HTTOP As Integer = 12
        Const HTTOPLEFT As Integer = 13
        Const HTTOPRIGHT As Integer = 14
        Const HTLEFT As Integer = 10
        Const HTRIGHT As Integer = 11
        Const HTBOTTOM As Integer = 15
        Const HTBOTTOMLEFT As Integer = 16
        Const HTBOTTOMRIGHT As Integer = 17
        Const borderWidth As Integer = 5
        MyBase.WndProc(m)
        If m.Msg = WM_NCHITTEST And m.Result.ToInt32 = HTCLIENT Then
            Dim p As New Drawing.Point(m.LParam.ToInt32 And &HFFFF, m.LParam.ToInt32 >> 16)
            p = Me.PointToClient(p)
            If p.X < borderWidth Then
                If p.Y < borderWidth Then
                    m.Result = New IntPtr(HTTOPLEFT)
                ElseIf p.Y + borderWidth > Me.Height Then
                    m.Result = New IntPtr(HTBOTTOMLEFT)
                Else
                    m.Result = New IntPtr(HTLEFT)
                End If
            ElseIf p.X + borderWidth > Me.Width Then
                If p.Y < borderWidth Then
                    m.Result = New IntPtr(HTTOPRIGHT)
                ElseIf p.Y + borderWidth > Me.Height Then
                    m.Result = New IntPtr(HTBOTTOMRIGHT)
                Else
                    m.Result = New IntPtr(HTRIGHT)
                End If
            ElseIf p.Y < borderWidth Then
                m.Result = New IntPtr(HTTOP)
            ElseIf p.Y + borderWidth > Me.Height Then
                m.Result = New IntPtr(HTBOTTOM)
            End If
        End If
.
In questo modo il form potrà essere ridimensionato normalmente. Se invece ti interessa solamente il codice per il ridimensionamento in basso a destra inserisci
codice:
    Protected Overrides Sub WndProc(ByRef m As System.Windows.Forms.Message)
        Const WM_NCHITTEST As Integer = &H84
        Const HTCLIENT As Integer = 1
        Const HTBOTTOMRIGHT As Integer = 17
        Const borderWidth As Integer = 5
        MyBase.WndProc(m)
        If m.Msg = WM_NCHITTEST And m.Result.ToInt32 = HTCLIENT Then
            Dim p As New Drawing.Point(m.LParam.ToInt32 And &HFFFF, m.LParam.ToInt32 >> 16)
            p = Me.PointToClient(p)
            If p.X + borderWidth > Me.Width And p.Y + borderWidth > Me.Height Then
                m.Result = New IntPtr(HTBOTTOMRIGHT)
            End If
        End If
    End Sub
.