see
http://archicad-talk.graphisoft.com/viewtopic.php?t=17043&postdays=0&postorder=asc&&start=130
for a discussion
from GS...
From the Connection pop-up, you can specify whether a local modem or printer port is used, or choose AppleTalk or TCP/IP protocols for network plotters. When TCP/IP protocol is selected, click the Setup button to enter the IP address (or fully qualified domain name) and port number of the desired network plotter.
However, I didn't do this. I use Plotflow. Plot to a spool folder and set Plotflow up as before. That wasn't changed.. yet. I would recommend Plotflow anyway. I haven't plotted directly from AC in years. Plotflow is great. You can spool to it, then shut down AC, or move on to another PLN, and the plotting continues.