Just out of curiosity, have you verified that in your network control panel, it's set to connect via Ethernet instead of one of the serial ports? Also in the AppleTalk control panel, set that to Ethernet as well.

You either have an incorrect setting somewhere or missing software. I have had about a dozen LC475s over the years with a variety of ethernet cards and operating systems and have never once had a problem connecting to any type of hub or switch. In fact the LC475 I have at the present is connected to my HP ProCurve gigabit switch and it works just fine.