FAA info
Basicly, if you have the minimum hours required for the rating you want, you will just fly with the instructor until you satisfy him that you are ready for test. All you need to start is a FAA restricted certificate based on UK certificate. For FAA IR you will get IMC in UK but not recognised by JAA. The poster has JAA CPL/IR/ME. Should be no problem and quite cheap. CPL/IR will be stand alone. If he has the hours go for the ATPL. Dont forget to get FCC radio licence and a BFR in the log book for the initial FAA PPL.
Regards NuName
CFI/CFII/MEI