Visual Basic

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    'This list will contain our textboxes
    Dim itemList As New List(Of TextBox)
    'Add each textbox to the list
    itemList.AddRange(New TextBox() { _
        txt1, _
        txt2, _
        txt3, _
        txt4, _
        txt5, _
        txt6})

    Dim rnd As New Random   'Random number generator
    For i As Int16 = 0 To lstListbox.Items.Count - 1
        'Pick a random textbox
        Dim index As Integer = rnd.Next(0, itemList.Count)
        itemList(index).Text = lstListbox.Items(i).ToString
        'Remove the textbox so we can't pick it again
        itemList.RemoveAt(index)
    Next
End Sub