bubba:
3 stages (not necessarly in this order)
1st Personnel interview. Why do you want the job, where do you see yourself in 10 years time etc etc etc. just like a normal interview.
2nd stage Technical Interview. The G-OP is right, if you knew everthing who would need CATC! Just have a good grounding and look motivated - make sure you visit a unit, airport and area if poss.
3rd Stage Computer test. This test reasoning, speed, decision making, following instructions etc. Some of it is okay some a nightmare - everyone is different. However everyone i speak to seems to think they failed this part - including me! The best advice to give is DONT GIVE UP. Just keep plodding through giving the answers, if you know one was wrong forget it and move on. I personally think that it is to see that despite what it chucks at you you keep going until it is over - day in the life of a tower controller really!
Lastly GOOD LUCK - let us know how you do.