I had a problem that sounds very much like you did. I'm using an ATI RADEON x1950 pro video card. I saw that there was a driver update on the ATI site so I d/l'd and installed the new drivers. They managed to turn Poser7 into an unstable mess. It had been running flawlessly for months before that. I rolled back the driver and still had problems.
I was able to resolve the issue by reinstalling the offending driver, and using ATIs software removal tool to get rid of the driver. THen I simply reinstalled the older, more stable drivers, and have had no problems since then. I don't know what type of video card your using. If its an ATI card then just follow my steps to repair the problem. If its a non ATI card then you want to do 1 of 2 things. 1. Find a software utilitiy from your videocard maker that will let you uninstal the driver completely (rolling back to the previous driver wont work), or 2. delete your videocard in your device manager and reboot your computer. It will find the videocard and ask you to supply drivers. Presto!
If you have any further need of assistance, feel free to PM me and I will try to be of assistance. Good Luck!