http://treasurechest.i2p/connect.html
In either case, connect as user adventurer with no authentication (if your client does not support 'no authentication', use a blank password instead). Going the proxy route, it's best to use a SOCKS proxy if your I2P daemon carries one ( i2pd has it enabled by default at port 4447; the Java-based I2P requires setup ). Otherwise, you can use its HTTP proxy, provided it supports the CONNECT method (I think both daemons do, and they both listen at port 4444 by default).