I know that the forums are full of this, but I haven't been able to find anything to get me to a complete solution yet. Standard "upgraded to Hardy, now nvidia driver doesn't let me boot into X" problem.
When running nvidia-xconfig or in any way enabling the nvidia driver, X would not start. After removing the nvidia-glx-new package and installing from the file from nvidia's site, I can run startx just fine and everything's dandy. Problem is, it no longer works when I reboot, and I have to reinstall the driver. I've tried stopping kdm first and relinking the gcc, g++ and cpp symlinks to the 4.1 versions (instead of 4.2), since the installer warned me about using a different version than my kernal was compiled with. Neither of those has worked. I've also tried installing nvidia-glx immediately afterwards, to no avail.
EDIT: BTW, envy doesn't work either.
EDIT2: Someone on IRC told me to add nvidia to my /etc/modules list, but that also failed to produce the desired effect.