I know I am stepping in late here....
Last time I used one of the free-dns tools, I remember there was a windows script that would run when I booted up my main system. The script would determine the _outside_ connection IP and update the free-dns record automagically. I have not used it in years, but it may be the same. Look on the FAQ's at the free-dns provider for info.
This way you do not have to pay for a static IP, and they can be expensive. (Not even sure Verizon will sell you one...)