Have you ever heard the term "DYNAMIC DNS"?
The most common use of Dynamic DNS is to assign a domain to a computer with dynamic IP address. A lot of companies offer free Dynamic DNS and tools. DynDNS is one of them. You just register a free account at their site and after that your asked for a Fully Qualified Domain Name (FQDN) for your server. With a few steps you assign domain name to your server with dynamic IP address. More specific with DynDNS you create an account and then you activate Dynamic DNS. You select My Services and then Add Dynamic DNS Host. In the new window you enter the host you want (e.g. myserver.dyndns.org). Now you must download DynDNS Updater and install it. This program is responsible to inform the name server of DynDNS every time your IP change. To configure DynDNS Updater read the manual.