@ Bads :
Assuming you are running windows
you download the DNS client here :
http://www.no-ip.com/downloads.php?page=win
Install it, using the domain name and log-in info you made when registring with NoIP.
Run the client program as a windows service, and it will automaticly keep your domain
up to date, with your _current_ IP adress.
On the webpages, you might be able to add some more details, like MX record,
or you *can* use it to manually updating your IP, or redirect it.
Quit simple actually
And the best thing is.... it works.