I second Brian304.
I have Rant XL Release 3 and it's excellent preparation for the IR. The IR is all about learning procedures and recognising what the ADF and VOR needles are telling you. Rant gives you plenty of practice.
I also have FSX with all the add-ons but would not recommend it for the IR or any other flight training.
IMHO the instruments on FSX are not clear enough to be of much assistance for instrument flying and in any case most of the aircraft in FSX which you might actually fly in the real world for training are not modelled with an ADF in FSX.
Learn the basics on Rant; learn how to fly the aircraft and the procedures in the SIM at your FTO.
