if you want to do this for free,
and don't mind having a sub-domain,
you can set up an account at one of many dynamic-dns servivces on the internet.
Even if your ip doesn't change, you can still apply for a dynamic-dns record.
http://hn.org/
is one I use for my site, and if you want to eventually upgrade to a full yoursite.com address, once you buy the address ($8.95/year at bigdaddydomains.com I think), hn.org will do the DNS for free. Those guys really rock!
you can get blabla.hn.org, or, for the price of a domain, blabla.com
so basically:
1) register an account at hn.org
2) sign in, and enter your ip
3) download and install a dynamic-dns tool to automatically check in with hn.org at specific times incase your ip changes, and to avoid automatic account termination.
Almost any dynamic-dns client tool that is shell based (or perl or python) will run just fine without any re-compiling under OS X. And the compiled non-script ones will just need a simple compile.
Post here if you need any help or have any questions!