I've done something similar without getting a IIgs ethernet card. If
you have a Mac with both a localtalk port and an Ethernet card, you
can run Localtalk Bridge (unsupported Control Panel from Apple) on the
Mac (OS 9 or earlier). I was able to mount a volume from a Unix box
running netatalk on the IIgs (despite the fact that the IIgs was not
directly connected to the Unix box) and transfer files quite easily.
This should also work for any other machine on the network running
Appletalk.
With a simple Google search, I was able to find the Localtalk Bridge
software here:
http://www.seismo.unr.edu/ftp/pub/mac/LWBridge2/
and here:
http://help.earthlink.net/techsupport/dsl/macpoet/html/localtalk.html
-Tilghman