The Open GL preview is badly broken in P7/Pro on some Nvidia cards. It broke about 5 driver revisions back, pre Poser Pro. I've talked to SM about this and we've seen P7 Sr3 and Pro Sr1 since and no fix...
I've been watching forums and it seems to crop up most with GeForce 8 and 9 series cards and Vista 32 or 64 bit. Usually shows up as a crash to desktop when moving the camera after loading a figure. I've also seen reports of it happening part way through a session but I suspect that's something else. I've spent hours prodding and fiddling various things and the easiest fix I've found is to load a simple prop first before attempting to load anything complex with lots of mat zones. Rotate the camera to make sure that Poser and the OpenGL driver have lined up their ducks and it isn't going to quit. Now load your scene or start a new one. Repeat when relaunching the program. I do this when I start playing and I can't remember the last crash I had. The preview settings in the program don't affect stability for me, just the usual speed/quality trade off.