Well, there is one book I've been using for reference that has definitely helped with the learning curve of Silverlight. They have a really good section on the different types of data access you can do from Silverlight, namely their coverage of WCF (my current favorite method). You can find that at...
Silverlight 2.0 in Action
Or... you can save yourself the trouble of ordering that for the time being and check out this blog by one of the Telerik people, it covers a simple setup for using WCF with Linq to SQL in Silverlight (this example being for TreeView):
Populating Silverlight TreeView from WCF Service with LINQ to SQL
That blog post will give you most of what you need to know currently for Silverlight data access in about 15 minutes, and with pictures. :)