Last week at MIX07 Nathan Buggia and I presented a talk on Search enabling dynamic web content applications including ASP.NET and Silverlight web applications. Download the deck and stream or download the video.
The BasicSearch.zip sample demonstrates how to use the SearchDataSource, search providers and turn your ASP.NET navigation into a search site map that can be consumed by the major search engine. Download the ASP.NET Futures CTP and copy the Microsoft.Web.Preview.dll into the bin directory.
You can find QuickStarts on Search and Search Site Maps to learn more. It will also show how to write your own search provider. I have included sample code search providers for Index Server and Yahoo! search.