DRI cannot work with the nVidia drivers. You do not need DRI to get any acceleration.
For the second question, see the README, right at the end of the FAQ section:
Q: I've installed the driver, but my Enable 3D Acceleration checkbox is still
greyed out! What did I do wrong?
A: Most distribution-provided configuration applets aren't aware of the NVIDIA
accelerated driver, and consequently won't update themselves when you install
the driver. Your driver, if it has been installed properly, should function
For the first question, what makes you think you don't have 2D acceleration? There is a RenderAccel option that might speed certain things up a bit, but it's experimental, and doesn't always result in a working X, so I wouldn't try it unless you have a good reason to. What's that reason?