I just spent a few hours scratching my head over this, because I woudl follow the instructions, and X would run straight after install but not after reboot.

At reboot the drivers mysteriously dissappeared.

1 remove the old Nvidia drivers,
2 install new kernel (or fix installed kernel)
3 install Nvidia drivers
4 remove the "checking Nvidia drivers script from all runlevels

THe script will reinstall the old nvidia drivers straight back over the top on reboot, otherwise, and screw up X completely.

Cheers,
Mathew