I'd eventually like to get a sample going, but want to point out that SDL Tridion does not have to take over everything or anything you don't want it to. So although you may have seen or written site Navigation logic that generates an XML or .sitemap file for an entire Tridion website, not all customers want or need SDL Tridion to manage all pages.
This MSDN article describes how to configure multiple Site Maps. The useful part for SDL Tridion implementations is:
You can use nested site map nodes, which means if you're using this XML file for navigaiton, Tridion doesn't have to take over your whole site or whole navigation. You can start one Structure Group at a time.