Comment 6 for bug 248055

The old "trick" won't work anymore because it is unnecessary since 0.96.4. Older versions wouldn't even start if they were too old. As of 0.96.4 you can use outdated versions for all eternity to your own and everyone else's disadvantage again. It will however not bootstrap - that is contact peer caches when its own cache is empty - any longer. Many or most of these peer caches have become defunct anyway since the last release as usual anyways.

If you don't remove your ~/.gtk-gnutella directory, it should be able to connect to the network just fine as usual. You should never remove your ~/.gtk-gnutella directory, especially not because of an update.
You can also always manually connect to other peers and therefore the network.

Regarding, "It also now says the client is firewalled". This is just the default assumption. As long as there are no incoming connections, gtk-gnutella has to assume it is "firewalled". gtk-gnutella has absolutely no knowledge whether you actually have any firewall activated. Thus, switching your firewall on and off won't be noticed by gtk-gnutella at all. The only thing that matters is whether there are incoming connections or not.

Now that doesn't mean you shouldn't update. You really should. However, old versions are neither banned nor defunct. After all a it just sits there like a web browser before you enter any URL. The only difference is that users seemingly expect it to connect on its own.