Drag & Drop da cartella a textbox

Private Sub tuaTextBox_DragEnter(ByVal sender As System.Object, ByVal e As DragEventArgs) _
        Handles tuaTextBox.DragEnter
    If e.Data.GetDataPresent(DataFormats.FileDrop) Then
        e.Effect = DragDropEffects.Copy
    Else
        e.Effect = DragDropEffects.None
    End If
End Sub

Private Sub tuaTextBox_DragDrop(ByVal sender As System.Object, ByVal e As DragEventArgs) _
        Handles tuaTextBox.DragDrop
    Dim str As String = CType(e.Data.GetData(DataFormats.FileDrop), Array)(0)

    ''Se ti serve solo la cartella fai così
    'str = IO.Path.GetDirectoryName(str)

    tuaTextBox.Text = str
End Sub