how to stop x-windows ?

I know the question has been answered before, but none of the suggestions I have found seems to work.
root problem: want to upgrade from ubuntu 11.04 to 11.10 and then 12.04, but (as I understand it) the unity desktop does not work with the generic graphic driver I have. it requires the appropriate driver for the card (nvidia quadro fx 500/f600/agp/sse2).
found the driver on the nvidia website and downloaded it, but cannot install the graphics driver unless I first stop the x-driver for the desktop.
so I went to open the command window:
<ctrl><alt><f1> produces a black screen with no prompt and no response to the keyboard, but
I was able to open the command window from applications->accessories
tried:
>sudo service gdm stop - did not produce any effect
>sudo /etc/init.d/gdm stop - stopped the x-driver, but also left a black screen with no response to keyboard inputs.
>sudo init3 - made no difference; at reboot the x-window came back as the login window
and sudo /etc/init.d/kdm stop is ineffective, too.
So, which other way is there to stop the x-driver? or maybe is there a way to install the graphics driver while the x-driver is active?