What I did when I needed to do that was restart in 'failsafe mode'. I have SuSE Personal 9.1, using the GRUB bootloader. It's an option on there.
I'm still a bit of a newbie myself, but as I understand it (only worked this one out earlier today!) as soon as the pretty (better than 256) colours start appearing, you're on the X Server.
Remember, you can't have a nice graphical user interface (GUI) without the X Server, so you're going to have to figure out how to carry out the entire process by command prompts.
As I recall though, NVidia kindly package their driver in a tasty self-installing binary, so you just need to give that an easy-to-remember name, stick it in an easy-to-remember place (I used my home directory, /home/nl) and login as root to execute it.
If any more seasoned Linuxerons consider any of this to be stupid (apart from the obvious stupidity of trying to install the NVidia drivers manually on SuSE) please feel free to say so (although some sort of constructive criticism would be appreciated...)
If you arse
using SuSE, you dont have to worry about shutting down the X Server at all - just go into YaST, find Online Update, and get the NVidia driver patch.
If it doesn't work at first, it might be because you're not running YaST Online Update as root... (but maybe I'm the only person dumb enough to forget to do that... who knows? In my defence, I'd only been using Linux for a couple of weeks...