Would those having done the first interview shed some light on their experience and questions asked? There doesn't seem to be a lot of information in this thread regarding stages anywhere beyond the Aptitude test.
It's pretty much a standard HR interview - why you want to be a pilot, family background, career background, current job, etc. Not much you can prepare for unless you count reviewing your intentions of applying for the job and knowing yourself well, in fact they didn't even ask me anything regarding their company bg.
They do ask things like what would your husband/wife think if you had to fly over to australia for a year (if married), what would you do if you didn't make it, why do you want to quit your current job, what kind of people do you hate the most, how do you think you rank amongst other candidates... and so on.
As for Stage 2 (after HR interview) it comprises of a Medical Check, Group Exercise, Tech Interview (the "Final Interview" as the Dragonair staff put it), ICAO test, and social lunch. Medical is done in central - height/weight/BP measurement, standard blood / urine test (they specifically mentioned testing for HIV), chest x-ray, optical, ECG, audiogram (they give you a headset playing different frequencies at different amplitudes and you press a button if you hear a sound).
Those who've done the tests correct me if I've left anything out.