You could make use of the LINQ to XML library
...anywhere, there are tons of examples here on codeproject that should give you an insight.
XDocument doc = GetDocument();
XNamespace s = "http://www.google.com/shopping/api/schemas/2010";
var query =
from product in doc.Root.Elements("entry").Elements(s + "product")
let inventory = product.Element(s + "inventories").Element(s + "inventory")
let price = (decimal)inventory.Element(s + "price")
let shipping = (decimal)inventory.Element(s + "price").Attribute("shipping")
select new
{
Name = (string)product.Element(s + "author").Element(s + "name"),
Condition = (string)product.Element(s + "condition"),
Price = price,
Shipping = shipping,
TotalPrice = price + shipping,
Availability = (string)inventory.Attribute("availability"),
};
var dt = new DataTable();
dt.Columns.Add("Name", typeof(string));
dt.Columns.Add("Condition", typeof(string));
dt.Columns.Add("Price", typeof(decimal));
dt.Columns.Add("Shipping", typeof(decimal));
dt.Columns.Add("TotalPrice", typeof(decimal));
dt.Columns.Add("Availability", typeof(string));
foreach (var product in query)
{
dt.Rows.Add(
product.Name,
product.Condition,
product.Price,
product.Shipping,
product.TotalPrice,
product.Availability
);
}