"dial-up accounts, and some dsl or cable modem subscribers, often get a different ip address every time they connect. although this allows your isp to serve a large number of customers with a small block of addresses, it means that your location on the internet is always changing. by automatically maintaining the relationship between your fixed name and the changing ip, no-ip free anchors you in cyberspace."

they also provide a program that sends notifies whenever one's computer's ip address changes (available for windows, *nix and mac os).