XMLdatasource and DropDownlist

What I intend to do is :
I have 2 dropdown list boxes , first one will display all the countries , and second one will display the cities according to the country choosen in the first one.
</p><p>&lt;asp:XmlDataSource ID="XmlDataSource1" runat="server"
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; DataFile="~/App_Data/CountriesXML.xml"&gt;&lt;/asp:XmlDataSource&gt;


The XML is
</p><p>&lt;?xml version="1.0" encoding="utf-8" ?&gt;
&lt;Countries&gt;
&nbsp; &lt;Country name="India"&gt;
&nbsp;&nbsp;&nbsp; &lt;City name="Delhi"&gt;&lt;/City&gt;
&nbsp;&nbsp;&nbsp; &lt;City name="hyderabad"&gt;&lt;/City&gt;
&nbsp;& ...