I wouldn't worry about it. The defaults should be fine. It should default to 8 data bits, no parity, and 1 stop bit. The only thing you need to chage is the speed. I'd recommend 38400 for a 68K Macintosh like your Powerbook. Just make sure that Zterm is configured for 8 data bits, no parity, and 1 stop bit. Select 38,400 baud (or whichever speed you choose) and make sure that flow cntrol is off. Uncheck hardware handshaking if it's enabled, and disable xon/xoff if it's enabled. It's pretty straightforward.
For more info about getty or inttab, do a man getty or man inittab from your BSD box. Or, you can get these man pages online with a quick Google search.