RedHat users may find the following tip from Panayotis Vryonis <vrypan@hol.gr>
helpful!

Here is a tip to intergrate HP720C support in RedHat's printtool:

Install pbm2ppa. Copy pbm2ppa to /usr/bin.
Edit "printerdb" (in my system it is found in
/usr/lib/rhs/rhs-printfilters )
and append the following lines:
----------------------Cut here
-------------------------------------------
StartEntry: DeskJet720C
  GSDriver: pbm
  Description: {HP DeskJet 720C}
  About: { \
           This driver supports the HP DeskJet 720C inkjet printer. \
           It does does not support color printing. \
           IMPORTANT! Insert \
                "- | pbm2ppa -" \
           in the "Extra GS Otions" field.\
         }
  Resolution: {600} {600} {}
EndEntry
--------------------------------------------------------------------------

Now you can add an HP720C printer just like any other, using printtool.

[Author's Note: The same should work for the 820 and 1000, but it hasn't
been tested.  Also, use the pbmraw GSDriver if you have it; it's faster. ]
