Hi Bobscrachy
I just pinged your domain and that seems to be responding. So it means that the dynamic DNS bit is working OK.
So the problem must lie in the port redirection on the router.
If I understand it correctly (I've used port redirection a few times) you need to set the router up so that all traffic to port 21 (FTP) is sent to the
local address of your ftp server. So if your FTP server is on the local address 192.168.0.2 you would set a port redirection of port 21 to address 192.168.0.2. I'm sure you know all of that
The only reason I can think of to make it go wrong is if the router or the FTP server have a firewall which blocks port 21. If the FTP server PC is running Windows XP, make sure that the built-in Windows firewall isn't blocking that port
Hope this helps.