I wonder if the Xircom would also work on a GeoBook (as the GeoBook's LPT-port is a little bit limited)...
According to the Xircom manual it will work on any parallel port, as far as I can see, and I am an old PC enginner educated in the DOS days, and I will say that I know the hardware configuration of the ports. The parallel port on the GPC is also limited, and run by the BIOS. IN geos.ini and net ini, there is a remark (REM) that the parallel port is run by the BIOS, in other words, by the hardware. Geos support is broken in that part, however I turned the parallell port off in both geos.ini and net.ini just in case. The question is if the geos version you have in the GeoBook will support the EtherPKT? I think you can use the ODIAPLHA.ZIP package found at this site. Pity, you live in germany, otherwise we could have tested it, but I think it will work, that is my guess. And you will not even need to have a Xircom adapter. I know that Accton etherpocket was very popular in germany, so you can try that if you can get it. BUT, I would advice you to use a separate power feed, not the power feed from the ps/2 port.
Another alternative is to use a PC-card Ethernet Adapter in the GeoBook if the PCMCIA slots works for more than memory cards. I have used a D-Link on a PC successfully (that eventually burned out, because of the unstable AMD CPU). D-Link with network cable. Orinoco Silver or Gold with wifi, but the support is limited nowadays with WEP 32 and 64.
BR,
Hans