Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
  System.EventArgs) Handles Button1.Click
        'Anbindung an DB
        Dim preloadData As New DataSet
        Dim con As New OleDb.OleDbConnection
        Dim cmd As New OleDb.OleDbCommand
 
        con.ConnectionString = _
           "Provider=Microsoft.Jet.OLEDB.4.0;" & _
           "Data Source=C:\Datenbank\Datenbank.mdb"
 
        Dim selData As OleDb.OleDbDataAdapter = New OleDb.OleDbDataAdapter _
        (("SELECT Kunden_ID, Name + ', ' + Vorname AS Vollname FROM Kunden" & _
        "ORDER BY Name"), con)
 
        selData.Fill(preloadData)
        cmbTest.DataSource = preloadData.Tables(0)
        cmbTest.DisplayMember = "Vollname"
        cmbTest.ValueMember = "Kunden_ID"
        cmbTest.SelectedIndex = 0
 
    End Sub

 Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As _
   System.EventArgs) Handles Button2.Click
        MsgBox("Kunden_ID = " & cmbTest.SelectedValue)
    End Sub

Private Sub cmbTest_SelectedIndexChanged(ByVal sender As System.Object, ByVal e _
  As System.EventArgs) Handles cmbTest.SelectedIndexChanged
        lblTest.Text = "Kunden_ID = " & cmbTest.SelectedValue
    End Sub