On the Robust Haven site there is a great, very detailed post explaining Isolated Storage and how to use it in Silverlight with a generic repository.
Isolated storage is a file system. It is called "isolated" because it is rooted to a specific directory which provides the sandbox required for browser security. [...]
Creating a base generic repository allowed me to centralize common IsolatedStorageFile operations that would be needed any time I wanted to save, retrieve, or delete any type of object from Isolated Storage in my application while still being strongly typed.