Thanks so much for the explanation and links, Richard.
I enabled the driver as described in the link.
Unfortunately my WinXP Sp2 does not like the connection. The installation finishes with: Cannot start the device ( code 10). No new network connection visible
I see some suspicious messages on the IT with dmesg. Unfortunatly, I do not understand USB protocols nor RNDIS.

The g_file* stuff works ok.