I had the exact same problem and fixed it by:

1. upgrade to the latest possible nVidia drivers
2. create a custom profile for poserpro.exe
3. disable all possible settings for the poserpro profile

later I found out on the Content Paradise message boards (I forget which post) you only need to change one setting in the nVidia control panel. After that, it worked like a charm. I'm on Vista64, but it would likely apply to XP64 as well.