I presume you're referring to TrackIR5? If so then yes it works fine with P3DV4. Just remember that if you've modified the TrackIR setup to work with EZDOC in FSX you'll need to rename the manifest files back to their originals.Thanks Dave.
I've only the question about IR5 holding me up from buying it now. I'm pretty sure it will but its not only a wonderful gadget for Flight simulation but a very costly one too so I'd rather not have to buy a replacement.