*** You might want to check in /etc/X11/ and see if there's an XF86Config file or an xorg.conf file. That might help you determine if you actually installed something.
But, not knowing if you even installed XF86, I would recommend the following:
boot to runlevel 3 (like you have a choice
log in as root
run pkgtool - "remove" packages option
Remove anything beginning with X11
Remove anything with XF86 in the name
Mount your cdrom with the /slackware/x directory on it
CD to that directory
run the following command:
installpkg --verbose *.tgz
(or run pkgtool again and choose "install packages from current directory")
Check your /etc/X11/xorg.conf file to be certain it matches your specs.
Run startx from the command line
Check for errors