If you bind your ComboBox to a DataSource, you can set any Field as DisplayMember and not bother with a ValueMember, just cast your SelectedItem like this...

Code:
Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
    Dim row As DataRowView = DirectCast(ComboBox1.SelectedItem, DataRowView)
    MsgBox(row.Item(columnIndex))
End Sub