You can boot into single user mode or text-only mode, make the necessary changes, and then boot back into graphical mode.
You can force booting into a specific mode when first turn on your computer by appending a number to the end of the
linux line in GRUB2 (or the
kernel line, in GRUB Legacy). When you boot your computer, press e at the GRUB screen (the screen where you select which kernel you want to boot). This will produce a GRUB menu editor containing the selected boot commands. Find a long line that begins with
linux. At the end of the line, add a number corresponding to the mode you want to boot:
1 - Single User Mode
3 - Text-only Mode
5 - Graphics Mode (Usually the default mode)
For problems with a graphics driver, it's usually sufficient to boot into text-only mode (i.e., 3). From here you can log in as your normal user, then become root and perform any administrative tasks that you need. This includes uninstalling the nVidia driver or recreating the initramfs as per the tutorial.
See Also (with screenshots): http://www.if-not-true-then-false.com/2012/howto-change-runlevel-on-grub2/
Alternatively, depending on how far your system makes it in the boot process, you may be able to access a text-only console without changing any boot parameters. Boot your system as normal and wait for it to make it as far as it goes. Then press ctrlaltF2. If your system has booted to a sufficiently advanced state and is not hung, you should then see a login prompt. Here you can log in as your normal user, become root, and then perform any administrative tasks to finish installing the nVidia driver.