<blockqote>The cable that I am trying to use has a 25 pin connector on each end.
Shut off the computer first, then remove the computer-end of the 25-pin cable. The only port on a Mac that has 25 pins and looks like a parallel or old-fashioned serial port is actually a SCSI port, and your printer will never work plugged into that.
The printer [serial] port on a Mac is a small round connector, reminds you of a S-Video jack. Mini DIN-8. there are two, right next to the keyboard connector. One is labelled with a print Icon, and the other with a modem icon. You can use an Apple Printer-8 cable, or you can use PhoneNet boxes and telephone cords. If you expect to have more Macs in the future, PhoneNet is expandable, the printer-8 cable solution is not.