I specifically want to go from ethernet, over a serial link, then back to ethernet?

The Netport will convert traffic to serial link across an ethernet connection so that you can put a serial device onto an ethernet network and see it over the network. If you had serial devices in between 2 ethernet connections the Netport will do this. The LAN06 takes its power over pin 9 or the LAN01 and LAN02 take their power from the adaptor.