<obout:SuperForm ID="SuperForm1"
         runat="server"
         DataSourceID="SqlDataSource1"
         AutoGenerateRows="false">
        <Fields>
            <obout:TemplateField HeaderText="Ship Country">
                <ItemTemplate>
                    <%# Eval("ShipCountry") %>
                </ItemTemplate>
                <EditItemTemplate>
                    <obout:ComboBox  runat="server" ID="ShipCountry"  DataSourceID="SqlDataSource2" 
                     AutoClose="false"  DataSourceID="ContinentsDataSource" DataValueField="ContinentID" 
                     DataTextField="ContinentName">
                    <Details>
                        <obout:ComboBox  runat="server" ID="CountriesCombo" DataValueField="CountryID"
                         DataTextField="CountryName"  DataSourceID="CountriesDataSource"
                         OnLoadingItems="CountriesCombo_LoadingItems">  
                        <HeaderTemplate>
                        COUNTRIES
                        </HeaderTemplate>
                        </obout:ComboBox>
                    </Details>
                    <HeaderTemplate>
                    CONTINENTS
                    </HeaderTemplate>
                    </obout:ComboBox>
                </EditItemTemplate>
            </obout:TemplateField>
        </Fields>
</obout:SuperForm>                               

protected void CountriesCombo_LoadingItems(object sender, ComboBoxLoadingItemsEventArgs e)
{
    if (!string.IsNullOrEmpty(e.Text))
    {
        int tryout = 0;
        if (int.TryParse(e.Text, out tryout))
        {
            CountriesDataSource.SelectParameters[0].DefaultValue = e.Text;
        }
    }
}

Sub CountriesCombo_LoadingItems(ByVal sender As Object, ByVal e As ComboBoxLoadingItemsEventArgs)

    If Not (String.IsNullOrEmpty(e.Text)) Then

        Dim tryout As Integer = 0
        If Integer.TryParse(e.Text, tryout) Then

            citiesDataSource.SelectParameters(0).DefaultValue = e.Text
        End If

    End If

End Sub