The location of the cups files varies. The ppd file needs to be located inside 
the CUPS ppd directory for them to work. Basically, copy them in, restart 
CUPS, and go into CUPS's web interface to configure the printer.

There are some contributed e-mails from selected users of their experience 
in this directory, and 8 PPD files; the PPD files should be left gziped 
when copied into the CUPS directory - there is no need to expand them.

CUPS < v1.1.13 and XPP = v.1.0, KDE 2.x, foomatic < 1.9 should use the 
*-cups.ppd's (the deciding factor is XPP version). Newer CUPS, XPP=v.1.1 
and KDE 3.0 should use the ones without *-cups*. 
(See http://www.linuxprinting.org/cups-doc.html for explanations).

The *usb* ones have 5700L USB printing turned on. The normal one
for 5700L only do parallel port. (These should be merged eventually).
The 5800L/5900L ones can do both. It is safe to have both (normal and +usb) 
of the 5700L PPDs simultanesously to the extent I understand it.

==========
Redhat 8.0:
    /usr/share/cups/model/

Mandrake 9.0, foomatic 2.02, 5700L (CS):
    /usr/share/cups/model/epson/   epl5x00l.ppd.gz

Debian 3.0:
    /usr/share/cups/model/Epson/ (Note the capital "E")
    (More info at: http://www.weejoker.demon.co.uk/epsonepl.html)

foomatic (downloaded directly from linuxprinting.org):
    /usr/local/share/foomatic

    cp driver/*  /usr/local/share/foomatic/db/source/driver/
    cp opt/*     /usr/local/share/foomatic/db/source/opt/
    cp printer/* /usr/local/share/foomatic/db/source/printer/
    cp -av Epson-EPL-*-cups.ppd.gz /usr/share/cups/model/