I assume you're refering to the HP82164 HPIL-RS232 converter.
It has a standard 25 pin RS232 serial connector. For the record, the DB25 parallel printer connector and the DE9 serial connector are really PC-isms (the latter came in with the PC/AT). The RS232 standard specifies a DB25 connector.
There is a jumper block inside the interface that you can plug in either way round. One way, the interface has the pinout of a DTE (so will link directly to a modem), the other way it has the pinout of a DTE (so will link directly to a terminal or computer). But I find the only way to remain (in)sane while using it is to leave the jumper at the DTE position and wire up the external cable appropriately.
The problem with that interface is that HP seem to have read the RS232 standard, and nobody else did :-). Which means that if you want to use hardware flow control (and I strongly recomend it), you have to wire up a special adapter.
You can find the wirelist of the adapter and some linux-related software in the distribution mentioned on
http://www.hpcc.org/datafile/hpil/lif_utils.html