The title is somewhat suggestive of the point I'm going to make here.
If you're using Windows 7 Ultimate (x64) then you'll probably want to wait for the final version before upgrading from the 197 drivers to the 256 version (if you plan to at all). POL would work, but once FFXI started and switched to the 3D pre-character Login screen it crashes. Other 3D applications (several emulators; Mass Effect) seemed to work fine.
Should you wish to test fate/bork your FFXI experience, Anandtech has links to Nvidia's beta driver page here.