What is the Cassini Web server?
The Cassini Web server is a simple, fully managed Web server that hosts ASP.NET. The Cassini Web server is a combination of the following: • A simple HTTP listener that was built by using System.Net.Sockets. 
• A hosting sample of ASP.NET that was built by using System.Web.Hosting APIs. This lets you host ASP.NET from any managed application.

If we are not using VS 2005 also we can built our web applications using this cassini web server.