Fred:
...
> I ran gpm-mouse-test again. That program seems to have major
> problems. It can't even detect the baud rate which I know to be 1200.
...

I tested it here and it succesfully detected my MouseMan at 1200baud.

It can be that your serial to usb converter confuses the program because
usb delivers bytes in a different way, in packets, not one byte at a time.

I might make a din-8 (aka sun mouse if.) to rs232 converter within the
month. If so I'll report back to you.

Regards,
/Karl Hammar