I ran Poser 7 under vista and after turning OFF uac had no problems with it.

The later versions of Poser should give you the option of installing content to  another folder to avoid the security issues.

The very latest video drivr may not be a good idea, I stay with an older version because it is more stable for my system.

You should treat the latest version as a new instal , you dont need to upgrade from Poser 5.