The ASP.NET OpenID web site (C#) project template isn't a tuturial, but it does create a functioning OpenID ASP.NET web site.
I just installed it and was able to get a site up and running. Here are a few gotchas that I ran into:
When you create a new project using the template, do not choose a deep path - this will create problems during database creation.
When you first run the application, you'll hit an exception - don't worry about it. When you get the YSOD, simply browse to the Setup.aspx page mentioned in the instructions.
If you don't have an OpenID, you'll need to get one. The initial page loaded after database creation has a 'Get OpenID' link if you need to get one. It's a simple process and only takes a few minutes.
Once you get through that, you'll have a working implementation of an OpenID web site.
You might also want to check out the DotNet OpenAuth ASP.NET Controls.
HTH
Edit
For anyone interested, there is also an ASP.NET MVC 2 OpenID web site (C#) template. I'm surprised @Andrew Arnott answered the other question and didn't mention these, since he is the author.