To use the plotter as a printer in OS X you will need an appropriate driver. You don't mention what plotter you are using so it is impossible to give you a detailed answer. Gimp Print with or without Ghostscript might work if your plotter is supported. Otherwise you should be able to easily set it up as a plotter over TCP/IP in PM. Just type in its ethernet address and port (typically 9100). AFAIK Appletalk is not an option.