Dave,
  You may try use next method, which not require PIC.It may be not
work absolutly propertly(in HPIL protocol), but in most case it
work right.Your HPIL device must be in 'trans. only' mode.
Of course, you may use PIC to connect device to computer.It is not
too hard, but i think that your work time is too expensive for it.

        HPIL                                      CENTRONIX
                       .---.
         D101 >--------|   o----------------------  DATA1
                       '---'

           .   .   .   .   .   .   .   .   .   .
                       .---.
         D107 >--------|   o----------------------  DATA1
                       '---'
                        04

         DAV  >-------+---------------------------  STROBE
             .--------'
             |
             | .--.
             '-|  o---.
               '--'   |
                    .-o---.
                    | CL D|--- VCC
         NDAC  -----|Q    |
                    |  CLK|-----------------------< ACK
                    '-----'
                      74
         NRED  -----------------------------------< BUSY

Sorry of my english.

Dmitry.
kozodaev@vxitep.vitep.ru