I've always just messed with /etc/X11/xorg.conf, but newer distributions, specifically Ubuntu, don't really use that any more. It might be easier to just go into his user profile as root (/home/username), grab his files and put them somewhere else, delete the user account and create a new one, then put the files back, and fix any permissions issues by running the following as root after you put the files back (replace newusername with whatever the username for his new account):
Code:
chown -R newusername /home/newusername
chgrp -R newusername /home/newusername
chmod -R 770 /home/newusername