Mac OS X has a built in Apache web server. All you have to do is execute the following steps to turn it on. You don't need to do the DynDNS part.
Using the IP address from when you set up the Apache web server, open a web browser, and enter your web server IP address. If everything is working, you will see a listing of your folders. If you have another computer on your network, open a web browser on the other computer and enter the IP address of your web server in the URL window. If your web server is correctly installed, you will see the same file directory in the web browser of the other computer. If you can't see your files from another computer, your firewall might be blocking it. Check your firewall settings and make sure Personal Web Sharing is enabled.