There are no prior requirements for taking the PPL / CPL / IR exams other than an "endorsement" from an Instructor - I don't know about the ATP. Most of the online-type training tools will provide them for you when you have finished. I used the ASA books and the associated QB - they were as cheap as chips and did the job just fine for me.
I did the FAA PPL, CPL and Instrument written exams in the UK with only 10hrs on fixed wing before I went to the US for the flying.
Last edited by this is my username; 2nd Jan 2013 at 18:10.