It is possible to connect the HP 200LX to a local area network (LAN) using a PCMCIA Ethernet card.
Since the PCMCIA slot is occupied by the card, all software that is used to comunicate via LAN needs to be installed on the RAM drive (C:).
For communication via LAN you may use the WWW/LX software suite by D&A software. You can find WWW/LX and its companion programs in the S.U.P.E.R. archive or on the D&A software website.
You can find an example of a quite complex WWW/LX configuration, that I used for many years and that includes usage of an Accton EN2216 ethernet card, here.
Another example setup – by Ted Heise – is described here.