I run Ryzom on Vista 64-bit with a Nvidia Graphics card.
One thing I changed is the installation location, instead of installing it in the default location I opted for installing it in my users home directory.
Second thing I did, was disabling desktop composition on starting the client.
Third thing was that I don't use the auto mode to determine the graphics engine used. You may want to try to force the engine to OpenGL (for Nvidia) or to DirectX (for ATI) and see if that improves your experience.
