*** SOLVED ***
For anyone who was having the same problem (on Slackware 10, anyway)....
When you install gs fonts, cups needs to know where the fonts are -- you can set this in /etc/cups/cupsd.conf.
HOWEVER, ghostscript also needs to know where the fonts are. If you do
the output will tell you where ghostscript expects to find its fonts. Make sure there are copies of all your fonts in the cups font search path, AS WELL as in the ghostscript search path shown in the gs -h output.
If someone has a specific question, or a better solution (mine can't be the best, there are copies of my fonts everywhere), drop a line here.