I have installed RedHat6.0 out of the box on a laptop with 3c589d pcmcia network card. The module is loaded (high pitch beeps), ifconfig says eth0 is up & running ok. I can ping myself, but no other computer (no respone whatever). The card does actually send something (I can see my hub blink...), but nothing ever gets back to the system. According to ifconfig it also receives packages. I observed the same symptoms with a Fujitsu network card.
Withdraw the report; a PCMCIA_OPTS="int_list=5" in /etc/sysconfig/pcmcia solved it... Obviously all netcards I tried were mapped to an "corrupt" interrupt.