2 sql database driven drop-down lists to link up

Development plaform: C# ASP.net 2.x, SQL 2005, MS Visual Studio Pro using Web Developer, IIS 6

Hi there,

I am trying to get these 2 sql database driven drop-down lists to link up.

i.e. depending on what the first drop-down list option is select will determine what the second drop-down list will display.  Essentially, fire-up another sql search for related records etc.

Below is the shell of the program -- these 2 sql-based drop-down menus are working fine independately -- just need to get them to link up.

Could someone please add to this scripting the additional coding I need to consider in order to get it working?

<asp:DropDownList ID="DropDownList1" runat="server" DataSourceID="SqlDataSource1"
            DataTextField="LeadSourceProviderName" DataValueField="LeadSourceProvider_ID">
        </asp:DropDownList>
        &nbsp; &nbsp;
        <asp:DropDownList ID="DropDownList2" runat="server" DataSourceID="SqlDataSource2"
            DataTextField="LeadSourceProviderProductName" DataValueField="LeadSourceProviderProducts_ID">
        </asp:DropDownList><br />
        <br />
        <br />
        <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:FORTUNEConnectionString %>"
            SelectCommand="SELECT [LeadSourceProvider_ID], [LeadSourceProviderName] FROM [LeadSourceProviders] ORDER BY [LeadSourceProviderName]">
        </asp:SqlDataSource>
        <br />
        <br />
        <asp:SqlDataSource ID="SqlDataSource2" runat="server" ConnectionString="<%$ ConnectionStrings:FORTUNEConnectionString %>"
            SelectCommand="SELECT [LeadSourceProviderProducts_ID], [LeadSourceProviderProductName], [LeadSourceProvider_ID] FROM [LeadSourceProviderProducts] ORDER BY [LeadSourceProviderProductName]">
        </asp:SqlDataSource>


Thank you in advance for your time and efforts with this enquiry.