Flyin'Dutch'
I returned from the USA a couple of weeks ago after going through the process of obtaining an FAA CPL/IR.
Before going I had a CAA PPL and a restricted FAA PPL based upon the validity of the CAA PPL. As the FAA certificate was issued in 1999 I had to obtain a letter of authenticity from the FAA so the Examiner knew my CAA PPL was valid.
Firstly I went through the FAA IR course, written test and flight test. Once passed the examiner gave me an FAA PPL that was still restricted (based on my CAA PPL) but also had Instrument Airplane (US Test Passed) written upon it.
I then used that FAA PPL/IR (still restricted in terms of validity) to obtain a full unrestricted FAA CPL/IR.
You do NOT need a full unrestricted FAA PPL before going for the FAA CPL Written and Flight Tests. However you will need your FAA restricted certificate based on your CAA/JAA licence and if it was issued before the new verification rules then you will need a letter of verification.
Good luck with the FAA CPL/IR.
Best wishes,
Richard.