Isolated storage is easy to use because it exposes the same stream-based model that's used in ordinary .NET file access. You use the types in the System.IO.IsolatedStorage namespace, which are a core part of the Silverlight runtime.
Silverlight creates isolated stores automatically. To interact with an isolated store, you use the IsolatedStorageFile class. You get the IsolatedStorageFile object for the current user and application by calling the shared IsolatedStorageFile.GetUserStoreForApplication() method, as shown here:
Dim store As IsolatedStorageFile = IsolatedStorageFile.GetUserStoreForApplication()
Usually, this gives you exactly what you want: an application-specific, user-specific location ...