I looked at my pile of 3Com Etherlink cards, and found these two notes:
3C-PC-COMBO-CBL (RJ45 + Coax dongle) -> works on 589D/E.
Foxconn 07-0408-000 0035 (RJ45 dongle, number on cable) -> works on 574BT.
I think I've tested these around and it shouldn't hurt trying, but it probably will only...