>> when I type the IP address directly into the browser, I get an error "The system cannot find the file specified."


It is quite natural. Your server has many Vhosts set up and the Virtual hosting is based on domain names. So if you just give the IP address the server will try to locate the file in the main server's document root.

As for the pages/images not getting updated, you may have a caching system in between you and the HTTP server.