To use a dynamic DNS system, register an account with http://www.zoneedit.com
Documentation on: http://www.zoneedit.com/doc/dynamic.html
download http://ddclient.sourceforge.net/
You will need to change the section for zoneedit near the bottom, plus at the top set the interval to what you want (from 300) and uncomment:
use=web
There may be a problem if the password contains punctuation characters