Paul Sheriff demonstrates two ways of using the CollectionViewSource to sort data. The first one is in XAML and in the second post Paul is using code.
If you are using Silverlight's ListBox control, you do not have to write code to sort your data. Instead you can use the built-in CollectionViewSource object in XAML to perform the sorting for you. This assumes that you are using a collection that implements the IEnumerable or IList interfaces.