Don't know if this helps, but are you using OpenGL or Sree for preview mode? And do you have an nVidia graphics card, specifically GeForce? I'm asking because I recently encountered a problem that involved Poser Pro and one of the dlls that are apart of the nVidia driver install—nvogl32.dll. And, yeah, I'm running the most recent driver update from nVidia.

Anyway, I'd try to switching to Sree and see if that helps. I'm running XP x64 and you're using Vista so I don't know how much help this next bit is going to be, but try getting into Event Viewer after Poser crashes and see if there's any other modules that might be causing Poser to crash. That was how I found out about the problem with nvogl32.dll, btw.

Sorry, I can't be of much help otherwise :(