One of the most persistent issues that appears in my mailbag is the problem where a user is unable to select the Printer port for a serial device (the Chooser keeps reverting to the Modem port instead). We have commented on this before and noted Apple's response. It seems worth mentioning again.
Essentially, you cannot use the Printer port for a serial device when AppleTalk is active. Making matters worse, simply turning off AppleTalk from the Chooser is often not enough by itself. You may also have to restart. Apple adds: "However, be aware that using file sharing or Apple Remote Access will make AppleTalk active again. In this case, a better work-around is to make sure the Apple Remote Access Client is installed, this grants a new option in the AppleTalk control panel. This new option is called "Remote Only", and choosing it will then route AppleTalk to that, freeing up your printer port for use by your serial printer."
As an irritated M. Bryan discovered, without the Remote Only option, you may be faced with having to restart your Mac every time you turn on file sharing and later want to print something. First noted in Mac OS 7.x, this issue remains in Mac OS 8.0, and is not reported to be addressed in 8.1.