http://denihil.i2p/guides/xmpp
after that, set your proxy setting to http proxy with address 127.0.0.1 and port 4444 if using the java i2p, or
a socks proxy with address 127.0.0.1 and port 4447 if using the c++ i2p
as the hostname (or “server”) , use the b32 address gkn5kifvnyfctecnskd2v6rs2ilb5zivrpofmwxsu33bdg4yknla.b32.i2p if it says the certificate doesn't match (or whatever) , just ignore it and continue connecting!