Hi, there are two different modes to wire a HDI30 adaptor (the square plug, that goes into the PB's mainboard).
One mode is to use the PowerBook in SCSI disk mode (you would call it »target disk mode« in recent computers). Obviously your adaptor cable is set up to support this mode.
The other mode is used to hook external SCSI devices to the PowerBook as a host (to use a scanner, printer, storage or network adaptor).
Just make sure you get the appropriately wired adaptor cable and you are fine. You might look for the small L-shaped kind of adaptor, which include the HDI30 connector on on side and a D-Sub 25 pin connector on the other side, without a flexible cable. This adapters are available with a switch that allows to preselect any of both wiring modes.
I hope this helps.
P.S.: If you have several adaptor cables of the wrong make, you may also splice the cable and rewire the appropriate pin correctly.