Have you checked to see you have the most recent drivers for your video card?
Have you intalled the latest Poser service release?  It is Service Release 3.
If not, when you do install it, first uninstall Poser 6, then reinstall Poser 6,
then before you open Poser 6 or do anything else, install Service Release 3.
Do these first before blaming the computer.
If that still doesn't help you may need more memory on your computer,
you didn't say how much you have.