Years ago I was using a HP500PS and Mac's (some OS 9 and some OSX) and we used the HPGL2 card. I think you should get the card regardless since you need to have it to add memory to the plotter. I would recommend maxing out the memory on the plotter while you are at it. With the HPGL2 card you will plot versus print to the plotter. At the time I was using the plotter the "ripping" software that came with the plotter was incredibly bad and incapacitated whatever computer was running it. Plotting was fast and easy and if you buy one other item (jet direct card) networkable. I would have expected something a little better out of the box but.....
Without the HPGL/2 card I think you are limited to "Printing". Check with HP on the latest plotter firmware and OSX print driver. They are downloadable. "Plotting" out of Graphisoft products is going to look for the HPGL/2 card. Hope this helps.
