I saw this last night (Tuesday) when it's supposed to air on Friday. If you have comcast on demand, you can see this before it airs under 'Nickelodeon'.
I think that, after this eppisode, the other nations have to start catching up with the fire nation technology-wise or else the war might be over sooner than they think without a happy outcome. I'm not going to say what their 'secret' was but it's pretty powerful and Ba-sing-se(sp?) was lucky that Aang and Sakka were there.
Speaking of Sakka, I liked his, "And, together, we're Team Avatar!" thing. It cracked me up xd