Hi Tim,
I have come a bad cropper with this, recently.
The problem is with GDI printers where the printer software (not drivers) actually lives in the computer and not in the printer. If you try to network using a print server then it doesn't work, because there is nothing in the printer to make sense of what is coming in.
Embarrasment maximus at a client's.
Generic printer servers may also give problems with some printers, even if they aren't GDI. The printer manufacturers have figured out how to ensure that only their (expensive) print servers work correctly with their printers.