I've been using Poser 7 and Vue6 in Vista 64-bit for several months now.  I've really only encountered 2 problems to date.  The first issue I had was when I attempted to merge my Poser 6 and Poser 7 runtime directories into one structure,  At that point, Poser wouldn't launch - fortunately I backed up both directories before that little experiment.  (--- As an aside, I really need to find a good program to completely reorganize my Poser libraries, the darned thing has become painfully unmanageable and it can be difficult at times to find the figures and poses I want for a given scene any more.)

The second problem is that I can't run Virtual Fashion in Vista.  Period.  That isn't Vista's fault, it's something to do with the Nvidia driver versions 100+ (I have the same problem if I upgrade my video driver to the 100 series in XP as well).  So I've kept a dual boot configuration on hand with XP 32-bit and older 97.xx series Nvidia drivers so that I can run that and any other applications I find to be incompatible.