Try
http://www.noip.com/ Paul, I use it and it translates my router's current IP to a name like Phaese.no-ip.org so you can use the name and the server knows your current IP as the router has the account details in the Dynamic DNS section and keeps it updated periodically.
I think you will (as mentioned previously) have to click on an email link they send you monthly to keep it active, otherwise look at the payment options to make the name permanent.
Cheers
Chris