How do I make the WordPress URL list posts?

I’ve had a main page on my web site that links to my blog forever. Recently I decided to let WordPress do all the work. I followed the instructions at Giving WordPress Its Own Directory. My WordPress address is http://mydomain.com/blog, and my blog address is http://mydomain.com and it’s working fine except for one thing.

If I go to http://mydomain.com, I get the “home” page that I want. If I use the sidebar to navigate to posts, my permalinks are working fine. But if I go to http://mydomain.com/blog, all that is displayed is “Error 404 – Not Found”. I want this URL to display my list of posts. I know this is possible because I have seen blogs that do so. What step did I miss?