I use several apps which are far more demanding on the OpenGL than Poser is and have no problems at all with the exception of one teeny little bug with one tool in LightWave Modeler.
Although it probably is a Vista thing, it's more like a combination of Poser and Vista and OpenGL, not just Vista.
I do have the same problem in XP x64 with the same card, and the latest Poser 7 with the latest patches and updates. It didn't happen prior to installing the latest Poser 7.2.something patch.