Just hit 'A' at the gurb boot prompt and add a '3' to
the kernel
commandline.
This should take you to a simple console. At which point you can login as root
and make whatever changes you want to your xorg.conf.
When you are ready to try them out, just run
telinit 5
which will try and take you up to init level 5, which includes X - If it works
great, if not, you can go back to the text console with the control-alt-F1
key combination, run
telinit 3
to go back to init level 3.
Chris