have a trawl through that lot, although they're equally likely to ask you why the infantry in genereal and not e.g. signals. Think about why you want to join the army, what do your parents think about it and what your strengths and weaknesses are. They're also going to ask about your hobbies, what you did at school, etc.
In terms of the rifles, best thing I found is to just look at the different roles, which one interests you the most and why. They aren't going to ask you much about the history, but it's pretty key to know basic stuff e.g. who Sir John Moore was.