спасибо Марко, наконец:
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Dim myGeoService As New net.webservicex.www.country
Dim myISOcodes As String = myGeoService.GetCountries
Dim reader As New System.IO.StringReader(myISOcodes)
If Not Page.IsPostBack Then
Dim mycountries As New DataSet
mycountries.ReadXml(reader)
DropDownList1.DataSource = mycountries
'DropDownList1.DataValueField = "value"
DropDownList1.DataTextField = "Name"
DropDownList1.DataBind()
End If
End Sub