Luckily, IP's don't change as often as you might expect for most ISP's.
I have registered a dlinkddns account and set it on the router's configuration panel. It is pointed to my actual IP, but it does not show the welcome page on my localhost. For the second case, your webserver might not be listening to your external IP address. If everything is alright, this is probably a port forwarding problem.
You may check out other alternatives searching for "AMP (solution stack)" on Wikipedia (I'm sorry, I can't post more links due to reputation issues).
Using an update client with your Remote Access (Dyn DNS Pro) or Dyn Standard DNS hostname allows you to make sure you can always reach your home network, because it makes sure that your hostname is always up-to-date with the latest IP address.
The update client runs in the background, so once you have it properly configured you don’t have to worry about it; you only need to remember your hostname to reach your files and services.
If you’re like many Dyn DNS customers, you have a dynamic IP address which changes periodically (monthly, weekly or even daily).