A lot of people on the sim forums seem to think TackIR is the best solution to headtracking. Everything is perfect, smooth, no crashes, and total compatibility. So I went to the NP TrackIR forum to see whats cooking.
http://forum.naturalpoint.com/forum/ubbthreads.php?ubb=postlist&Board=44
It appears all isn't right with TackIR and that there are quite a few posts about all sorts of issues. So IMO, this makes more sense to take the time to give a freetrack system a try before investing in TrackIR as TrackIR has its issues also.