PPD files from Xerox

CentOS 4 running CUPS.
Where are the available ppd files used by "printconf-gui" stored?
I need to add a PPD via "lpdadmin -d myprinter -P myfile.ppd"
If I later run "printconf-gui" I believe it will wipe out the
myfile.ppd "driver".

I would like to add myfile.ppd as a "printconf-gui" driver selection.

Or

Xerox publishes ppd files for their products. What is the
best way to use the ppd's?

1) lpadmin via command line.
2) Xerox has their own printer manager.
3) http://localhost:631 ESP CUPS Admin.
4) Redhat "printconf-gui"

I lean toward no 3 above. If I pick 3,
I can copy non-Xerox PPD's from /etc/cups/ppd.
It would be good to be able to use the ppd's already
available my system, if I knew how.
.