IOExperts (http://www.ioexperts.com/) has drivers for some PCMCIA cards under Mac OS X. I have a Farallon 11Mb/s card which works fine with the driver but it isn't recognised in Airport assistant and doesn't support 802.1X (WPA encryption/authentication). The IOExperts driver hasn't had an upgrade for quite some time now and only the 1-month demo is free iirc.
I recommend searching for a PCMCIA card that gets recognised as an Airport card. I believe some Orinoco/Lucent and Buffalo cards are like this but I'm not sure because it is some time ago I was looking into this stuff and I gave up.
I just bought a 100' cat5e cable. Next time I buy the tools and make it myself, (I've had to do it in Network Admin). I mean the 100' only cost me $12.99 -darn good price