Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
  System.EventArgs) Handles Button1.Click
        MsgBox(ComboBox1.Text)
    End Sub

Private Sub ComboBox1_Enter(ByVal sender As Object, ByVal e As _
  System.EventArgs) Handles ComboBox1.Enter
        Button1.Select()
    End Sub