Hey ff09727,
Congrats on getting the call! I've been following your past posts a little bit, because it seems that we've both been going through the same stages of this process. I believe we both attended the same exam session back in October as well (IIRC?!?). I also got a call for the 2nd interview and will be doing mine in a couple of weeks. Looking forward to it!
Naturally I've been doing a little bit of poking around to see if there's any info out there about the structure of the interview, but honestly, I look at this, kind of in the same way I looked at the exam. There's probably not much you can do to prepare for the dialog of the interview itself. The whole process seems very much geared towards identifying aptitude and suitable personalities.
My advice; shake of the nerves, grab a hold of your head (that spinning can't be good for your neck

) go in there, be yourself, answer their questions with concise answers, be well spoken, relaxed and respectful. Also have some questions that you would like answered in the back of your head. Many might get answered during the course of the interview, but having a few in mind isn't a bad idea.
One last piece of advice. Try and dig around and find out a bit about the company itself, learn about its structure, operations, etc... That'll show that you have taken interest in the career beyond the actual job you are applying for.
And lastly, GOOD LUCK!
I hope (for both of our sakes) we'll end up running into each other in training some day!
Cheers!