become root. (su)
copy your fonts into a suitable directory. /usr/fonts is a good choice, make a subdirectory perhaps, (mkdir /usr/fonts/myfonts)
cd into the directory and run
/usr/bin/X11/mkfontdir
/usr/bin/X11/mkfontscale
at this point two new files, fonts.dir and fonts.scale should be created, by those commands.
All you need to do is add this new directory to you X config file. open /etc/X11/XF86Config with your favorite text editor, and locate the lines which are like
FontPath "/usr/share/font"
etc.
Add your own newly created font directory in there :
FontPath "/usr/share/font/myfonts"
and restart X. Have fun with your truetype fonts
PS: These instructions are for slack 9 (that i run) , and I do not have any idea if they would work in 8.1 , so sorry if they don't