After some tweaking, I found the following were necessary to get the Intel CardBus card working at 100bT half-duplex:
1) Moved /etc/rc.d/init.d/pcmcia.N to /etc/rc.d/init.d/pcmcia
2) Remarked out "SCHEME=" from etc/rc.d/init.d/pcmcia
3) Forced the card's media type to 100bT half-duplex by adding the following to /etc/pcmcia/config.opts:
module "tulip_cb" opts "options=3"