Jeff Prosise has a written a great sample and article for the February edition of MSDN magazine that walksthrough the new SQL Server based provider he built for the ASP.NET 2.0 Site Navigation System. This enables you to store your site map structure in a database instead of using the default XML Provider that comes default. Enabling it within an ASP.NET 2.0 site is as simple as configuring the provider in your web.config file -- no code needs to change in order to take advantage of it (and you can databind any page control to it using the new SiteMapDataSource control).
What is really cool about his provider is that it also uses the new SQL Cache Invalidation feature to cache the sitemap structure in-memory within ASP.NET (avoiding the need to hit the database each request to retrieve the data), but automatically regenerate it anytime the site-map structure changes in the database (ensuring that your site structure is always up to date).
You can read all about it and download the code from here.
Here are a few of my past posts on the new ASP.NET 2.0 Site Navigation system if you are interested in learning about it more:
Hope this helps,