Ok, IFR is a little easier to explain. VOR to VOR isn't possible because nobody is going to build them in the middle of the ocean, so instead we use North Atlantic Tracks (NATs) which are a series of Latitude/Longitude waypoints. You can find the current tracks on simroutes and add them too your flightplan then download it into fsx fairly easily. Or, if you're using a aircraft with a programmable fmc you can plug in the data there.
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