Using the CD, at the boot page press "F4" and select "safe graphics mode". You should then be able to boot up graphically and install from there.
To enter commands, open the "terminal" program found under:
in the upper left hand corner of the screen.
Alternatively, you can press the keys ctrl+alt+F1 to get to a command-line only runlevel. You can return to the graphical desktop by pressing ctrl+alt+F7.
To navigate to directories, use the "cd" command. For example:
will put you in the directory /etc/X11. Once there, you can list files with the "ls" command:
You should see your xorg.conf file there. To edit it, use "nano":
sudo nano xorg.conf
save changes by pressing ctrl+o and exit nano with ctrl+x
Hope that helps.