Mainly for reference, maybe it's useful for someone else:

* Have a Nikon GP-1 GPS Unit
* Plug a miniUSB-USB cable into the unit and your Mac
* Get gpsbabel
* You don't need any other drivers or programs
* run it on the commandline with

gpsbabel -T -i nmea -f /dev/cu.usbmodem3d11 -F gps.csv

and it prints the coordinates to the output. gpsbabel has many output formats, with eg.

gpsbabel -T -i nmea -f /dev/cu.usbmodem3d11 -o kml,points=0,line_color=640000ff,max_position_points=10 -F gps.kml

you get a KML file, which you can open with Google Earth.

Google Earth is by the way also how I found out the needed parameters, since it "just worked" there. I started Google Earth and its Realtime GPS feature and looked at the process list with "ps aux" and got, what I needed (especially the "/dev/cu.usbmodem3d11" parameter may be different on your Mac)