ok, ill try to explain how this could work. it works similar to no-ip.com's system, basically you have register a nickname/username with the system, and set a password, once this happens, the system will give you a subdomain address like bf6r45js90tyjvr.limewire.net/com or something. (i personally would use the .net for it, or buy another domain or something.)

then when the user wants to login, he needs to use his user/pass he used during registration, then it will update the system to his new ip address. then all a contact/buddy needs to do is keep his dynamic-dns name. nothing else will be needed for this kind of system. this kind of system of authentication does not need to be a distributed form because it is not at all running on the gnutella network. BUT the dns-system and its servers should ONLY be used for the authentication part and IP updates. everything else like chat sessions should be direct connections.

basically its just like the no-ip.com free service.