nope, easier - I have the following aliased as 'ddu':

    lynx -dump -auth=user:mypass "http://members.dyndns.org/nic/update?hostname=myhost.dyndns.org

I have 'ddd' set it to a random IP, so that I can determine when it is active and not have to deal with random proxy scans etc.

If you aren't UNIXy you can use one of the dozens of update clients:

http://www.dyndns.com/support/clients/

dyndns is just one provider. you could host it yourself. There are dozens of routers and clients that support DDNS protocol, no need to reinvent things.