Basic XML App

Hi,
     I need to write an app to total some data and I'm not sure where to start! Any advice would be appreciated.
I can get the data in Html, xml, csv or text. With that said XML is what I'll present it in here.

1    <Items>
2        <Item>
3            <ID>821</ID>
4            <Price>100000</Price>
5            <Person>Denis Hoctor</Person>
6            <County>Dublin</County>
7        </Item>
8    </Items>

What I need to do is create a list where its split into Counties and for each County I have a list of agents with the total number of times ...