The second way to configure X is to use xorgsetup, an automagical configuration program that comes with Slackware.
To run xorgsetup, log in as root and type:
# xorgsetup
If you've already got an /etc/X11/xorg.conf file (because you've already configured X), you'll be asked if you want to backup the existing config file before continuing. The original file will be renamed to /etc/X11/xorg.conf.backup.