No, if you mean both in the same LAN (e.g. at home) and want to trade with each other or internet.

But you can't download from other servants behind another NAT router. The Gnutella PUSH does not work if both sides are masqueraded/firewalled, because both can't handle incoming TCP connections (the NAT router has no idea how route/map such new incoming connections). One solution are explicit forwarding rules for every client in the LAN, plus using a FORCE_IP feature in your client. It will also improve your download success. Another solution would be a using a Gnutella proxy or NAT addons, but we do not have such things yet AFAIK.

PS: How about Gnutella clients using an traditional Socks 4/5 proxy, will they handle new incoming connections correct? Hmm, I guess not.