When I try to install the driver, the installer claims that X is
running, even though I have exited X. What is wrong?

The installer detects the presence of an X server by checking for
X's lock files: /tmp/.X[n]-lock, where [n] is the number of the X
Display (the installer checks for X Displays 0-7). If you have exited
X, but one of these files have been left behind, then you will need
to manually delete the lock file. DO NOT remove this file if X is
still running.