I'm having the same problem with Mac OS 8.6 on a Performa 6360, and for a similar reason--trying to connect to the Internet via free neighborhood wifi using a broadband gateway device vs. current AOL dialup. The "Connect via Ethernet" option is not showing up in the TCP/IP (and AppleTalk) control panel. The staus light on gateway is lit, showing good ethernet to the Mac, and the two 100 lights are steady lit on the Apple 5A0025 PCI Fast Ethernet card. Everthing I've found so far seems to say that the "Connect via Ethernet" option must be chosen in the TCP/IP control panel for regular ethernet, not AppleTalk/EtherTalk, to work. All the 8.6 ethernet extensions and Open Tranport 2.x stuff are enabled. Any other thoughts anyone? Thanks.
Fixed it! Bad card! I found and installed another recycled Apple PCI Fast Ethernet card for a buck, and "Ethernet" now shows up as a choice in the TCP/IP control panel. I got my free neighborhood wireless internet to work through a Buffalo ethernet adapter and my wife is happy with her much faster then dialup AOL email on her vintage Performa 6360 with TV tuner.