URGENT URGENT: Chained Listboxes - Data hierarchically in xml file

I need to display three chained text boxes with data coming from an xml file.? Selecting an item in the first text box would drive the list in the other text box. The data comes from an xml file, it is organized hierarchically. See the UI design and the sample xml file in the attachments. It has to be done in ASP.NET? C# with AJAX, preferably using .net only libraries.