The plotter is an HP DesignJet 300. It is connected to the network using an HP JetDirect EX interface. The printserver's IP address is 10.13.0.50. Please don't change the printserver's IP address or configuration, it is not at fault.
Not sure about Macs. Based upon what's in the Use the Printer HOWTO, this seems pretty straightforward. Just know that "port 9100" is the protocol to use, and if it gives you a choice between PS and HPGL, use HPGL.
On a Windows box, you need to ignore the temptation to click "add a network printer", and instead, "add a local printer", then "create a new port", then port type "standard tcp/ip port", then enter 10.13.0.50, and everything else should be sensible.
Since this is an older plotter, HP is no longer writing the drivers for Vista and later versions of Windows. However, there is a set of drivers available for Vista and Windows 7 here: http://www.mediafire.com/?njmtmnizmjm Use them at your own risk!