It's much easier to install stuff using apt-get (command-line) or synaptic(gui)

https://help.ubuntu.com/6.10/ubuntu/desktopguide/C/add-applications.html

Edit:
Another way to boot without the graphical shell is to choose the "recovery mode" option from the boot menu

And another way to install the latest graphics drivers is use the Envy script: (works for nvidia and ati)

http://albertomilone.com/nvidia_scripts1.html