Two observations.

It is not clear to me from your OP whether you are seeing blank patches on your screen, or if you only see a cropped version of your final image.

If it is the first, try turning your threads back to "1" for a test render. I had an AMD dual core processor once that had a bad core. It rendered fine with one core, but failed about half way through a render using two.

If the second, I'd check to see if the image size you are specifying is larger than you have your screen resolution set.

Finally, I strongly suspect the whole problem is your video driver. You state you stopped updating it. This is the kiss of death for Poser. Get the latest driver, install it, and try another render.

My own experiences with bucket size mirror the others. Acceptable buckets are 8, 16,32,64,128, and 256. 64 is my standard, but I've got a 64 bit OS and 8 Gigs of Ram.

Good luck.