Cam,
Take a good look through the 'sticky' above - all three stages are well explained there (although it will take you a while to read). From memory, Nokio's post on p22 is good for Stage 1 and there's a very good post on p155 for the newly updated Stage 2. Stage 3 coverage is a bit more patchy since a) not many people make it that far and b) everyone's interview is different.
As for those who are already ATCOs, they will have had a different application process to you - especially since Stage 2 has been redesigned in the last 2 months or so. They're brilliant for answering questions about the career, just less so about how to get there...