I was doing some ASP.NET MVC this weekend, and I couldn't get the project to start: all I got was "Internet Explorer cannot display the webpage", when using Visual Studio's built-in development web server (Cassini).
I think it's because Cassini doesn't support IPv6, and on Vista, "localhost" refers to the IPv6 address ::1, rather than the IPv4 address 127.0.0.1.
If you use http://127.0.0.1:12345/Home/, then it works fine.
To resolve this, you can go to the project settings and set the Start URL explicitly.