Did the conversion from FAA to JAA IR in August / September. It's 15 hours minimum (up to 5 of which can be FNPT1 if I recall). Pretty much got through it in the 15 hours, and hadn't flown IR since passing the FAA test in July 2000. I had about 250 hours TT when starting the conversion.
The FAA IR will give you a good enough grounding on the holds / approaches which differ very little. NDB holds are a lot easier than those VOR and FIX holds you do in the states. On the FAA IR you get unpublished holds on VOR radials at DME fixes which you don't know about before you set off. They are a real pain because you have to work them out a few minutes in advance with entry / wind correction etc... not fun when you're bouncing around in moderate turbulence and still maintaining +/- 100ft!
The R/t is a lot different over here and that was a bit of a hurdle for me, but I pretty much got over that doing the CPL before the IR itself. Also worth noting I went straight onto the IR conversion from the CPL course in the very same aircraft which helped a lot.