Apple ][ have no std serial port.  With expansion cards you can give
them a serial port but not an appletalk port.  The ][e came with a 
serial port (I think) or with card for it.  So the best you can do
with them is to wire null modem serial lines to a terminal server
or 16-port serial card deal.

If you have old Mac+ you can run localtalk or phoneNET and use
appletalk to do real networking with any macs.  You MIGHT be able
to do with apple ][gs.  However, to talk to this network with a unix
box you'll need hardware to do the appletalk<->ip conversion like a
cayman gatorbox or a shiva fastpath.  These boxes don't appear to be
cheap but maybe a donation from someone upgrading to a cisco?

To recap, no PPP on apple][, just dumb terminals.  Lots of wires,
and a multiport serial board in the unix box.  Hardware needed to
link up appletalk to unix.

-j