Coincidentally, this morning I was doing the exact same thing as this fellow. I had installed 9.10 on a Dell GX620 with an nVidia 6600, and needed to stop X in order to compile and install the driver.
I had already downloaded the Linux installable from nVidia, and found this excellent tip for getting in and out of the GUI:
To stop gdm from virtual console (after going to virtual console by giving Ctrl + Alt + F1):
sudo service gdm stop
To start after installing nvidia drivers or whatever we did in console, to start it is as simple as stopping
sudo service gdm start
<ctrl-alt-f1> drops you to a console login, but gdm and X are still running in the background, and nVidia drivers will not load until gdm is stopped.
Restarting gdm will bring you back into your Gnome X session. Alternatively, if you were just doing some work at the console and want to return to your X session without restarting gdm (which closes all your windows and programs, etc), just press <ctrl-alt-f7> to return from the console.