Gamers with previous generation GeForce GPUs, including the 8800 GT and above, are encouraged to download these new drivers as well.
Does that mean the new driver will not be compatible with the 8600 (and below) anymore?
No, the 310 series drivers are for GeForce 8xxx and newer.
The Support for GeForce 6xxx and 7xxx was droped and are now supported by the 304-drivers branch.