Ray, I'm not sure, but I _think_ the MG-I may be MG-III compatible.
I took a look on Dave Lane's site, and found that he's discontinued
the MG-I for lack of parts, but he does have an on-line manual:

http://www.nova-astro.com/pdfs/mgi.pdf

The bottom right corner of page 3 states: "If the GUIDE mode is
entered without previously having done an alignment, the _TheSky_
compatibility mode is entered. In this mode, the current telescope
altitude and azimuth are transmitted via the serial RS-232 port
whenever requested from a connected computer. Pressing any
key will return to the MAIN mode."

Now, this is a circa-1993 doc. I think that back then, the
only thing _TheSky_ supported was the Tangent Instruments
spec, a.k.a. MG-III and JMI/NGC-Max. I'd give it a try in that
mode; if it fails, I'll give Dave Lane a nudge and see if I can get
comments from him.

Meinolf, thanks for the bug report about datasets when
swapping languages. I recently realized this was happening,
when testing an Italian-language version of a user-added
dataset file sent in by Giuliano Pinto. I'd set various parameters
(magnitude limit, color, labelling) in English (or Italian),
swap languages, and see the changes vanish.

It has been present for a long time. Most people probably
run Guide in only one language, or didn't encounter this
bug, or figured "Bill must already know about it". I didn't.
But now I do, and I've fixed it, and the fix will be available
the next time I post an update.

-- Bill