There's nothing you can do to prepare for the tests, other than get a decent sleep beforehand. Those that pass are then interviewed for an hour. It's a behavioral interview, so Google it beforehand and practise it.
I've been on the panel a few times over the years, and tell you what, there are some very strange people who pass the aptitude test who have some very strange ideas of how to impress an interview panel We're looking for stable, level-headed, intelligent people who can string two words together with multiple syllables. We're not looking for mature-age boys who get their mums to do everything for them. (My experience is that the girls are a better bet for training. They're used to working 110% to prove themselves equal to a man, and they set themselves high standards. The guys want to coast, and it ain't that kind of course.)
You don't have to know much about ATC but what efforts have you made to find out? Minimum level of interest would be to arrange a visit to your nearest ATC centre or tower. Too far away? Conflict with your footy practise? Wrong time of the day? Car broke down? Don't know the email address? Get real. These are all actual excuses. Save the panel the effort of crossing you off the list.
The courses consist of 12 trainees usually. I expect at least 6 courses for 2010. But I don't work in Airservices much maligned - and rightly so - planning department!