I have setup a dyndns.org address for my network (eg mynetwork.dyndns.org), and have forwarded port 8201 to 478 on my TC. I cannot seem to connect this, either through the finder window, not through 'connect to server' where I put in "mynetwork.dyndns.org" or mynetwork.dyndns.org:8201.
Are you correctly testing the access using a remote connection.. ?? You cannot test this inside your own LAN.
Forwarding port 8201 to 478.. why?
BTMM uses
Ensure TCP port 5354 and UDP ports 4500 and 5353 are open on your firewall. To learn more about ports used by Apple products, click here.
At least according to this apple doco. http://support.apple.com/kb/HT4907
Because the TC is bridged.. it cannot open those ports dynamically and the Mac which you have setup for BTMM will grab them anyway. The TC will not work in bridge with BTMM.
So I think your whole setup is wrong.
If you want to do this manually.. which btw is far more likely to work.
Setup port forwarding in the dlink port 548 TCP .. ie that is AFP. And that is the only protocol that will work. Direct it to the TC.. do not port translate.. just do straight port forwarding.
Make sure you setup the dyndns in the dlink so it has the public IP registered correctly.. double check this.
Make sure the firewall is off in the dlink.
Make sure you have a decent disk password on the TC.
Now access the TC from a remote location.. by doing the finder.. go .. connect to server.
AFP://dyndns.address
You can even test it directly with the current IP to make sure.
As long as the dlink is working and the TC is correctly bridged.. there is no other setting required on the TC.