Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    Button1.Text = "Ограничить мышку"
    Button2.Text = "Отпустить мышку"
End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Cursor.Clip = Me.RectangleToScreen(Me.ClientRectangle)
End Sub

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
    Cursor.Clip = Nothing
End Sub