Also, just a follow-up thought, mraroid, I don't have a Network Control Panel on my 7.6.1 install.  I remember that being something optional.  Hmmm, but Wiki says Ethertalk was a standard released in 87 with the Mac II (and possibly SE) that included a Network Control Panel that allowed selection of built-in Localtalk or Ethertalk.  So you probably have to select EtherTalk if you plan to connect to an AppleTalk network via the ethernet card.  (Ethernet is built into the PM 7100.)

LEM says EtherTalk was just Apple's name for AppleTalk over Ethernet (which is what I had been remembering).  Let us know what happens.