Whitelighter- Stage 2 is just computer tests. They are very straight-forward and there is little you can do to practice for them except for brushing up on your mental maths skills. It is a very casual setting- you can go in comfortable clothes rather than interview style clothes. The tests take most of the day but you get lots of breaks. Don't bother trying to judge your own performance either. The guy i was sat next to said he found all the maths really easy- and he finished all his tests way before me. I thought i had done really badly because i kept missing questions but it turned out i passed and he didn't.
Good luck- just keep calm and if you miss questions don't worry.