You might put them (as root) in /usr/X11R6/lib/X11/fonts/... Type1 or TTF subdirectories or the equivalent on your system. You can open 'fonts:///' in Nautilus to see the list and samples.
I see all sorts of stuff on adding fonts and mkfontdir and whatever but I find that putting the fonts in the X11 fonts directories is all I need to do - almost.
I have one or two postscript fonts that don't show up, even with the AFM. PFM, PFB etc files in place. I am also having character set problems on some fonts I have yet to figure out (looking at, maybe, language settings?)
For instance, I have a Futura Typo/2 font that only shows the italic face and bullets in the font don't show unless I pick the document up in Windows (using OO).
There is something here and I am missing it. In fiddling around I messed up the X windows fonts once and couldn't restart X - made for a good excuse to reinstall as I had also messed up the printer, too (trying to get printer options so I could see and set them).
I am still using OS/2 as a standard for comparison...