I did some work on the plotter. Serial communications is working OK. I was able to control the plotter from a laptop using basic GL commands and draw shapes etc.
There are two outstanding problems:
* The plotter really likes German. There is an option to change the language to English (hold down a key on startup) but when it works, the setting isn't retained, and it mostly doesn't work at all. Luckily German isn't too hard to understand...
* I wasn't able to get a working Windows printer driver for it. There is a commercial driver that I tried (very expensive) but even it didn't work. I'm pretty sure this is mostly about finding the correct driver, and it may well be that using Linux or even an older version of Windows might be more helpful.