I have one of those ethernet to Assante localtalk/ethernet adapters and there's some fine print somewhere that it's missing some automatic recognition thing or something on the ethernet side. (can't remember exactly). But this makes it incompatible with many routers. Mine would only work if I used a 4-wire patch cable to the router or an 8-wire crossover cable directly to a Mac.

Watch the Tx/Rx lights and see if they are bouncing back and forth to verify the ethernet side.