If you register a domain with EasyDNS, you can use dynamic IP mapping (i.e. use your cable/DSL connection with a varying IP and map it to a fixed domain). However, there is no Mac OS X client to update the IP on connect on EasyDNS's web site.
I created a client that works perfectly with OS X. You need to use the command line to set it up, but after that you are fine and will likely never see it again. It's available for download from the EasyDNS page of my website.
[Editor's note: I use DynDNS.org for my dynamic IP naming, but if you use EasyDNS, you may wish to try Novajo's client.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020516092133847