Much of the OpenGL "software stack" often runs within the kernel for efficiency; but, yeah, that means any bugs in the code can cause computer crashes -- something that application bugs (as in Poser) cannot do for Windows XP or Mac OS X. That certainly is a risk. You'll generally be better off with the most recent generations of video card, simply because those are the ones likely to get the most attention and testing for any version of the driver. And Apple doesn't write the graphics drivers -- the card vendor does. It does appear to be true that ATi and NVidia have paid more attention to optimization on Windows, which is unfortunate. But while the difference in rendering speed is measurable on Doom 3, you're highly unlikely to be able to notice any difference in Poser previews.