Do 802.11b PCMCIA cards provide for an external antenna?
Just a few manufacturers provide this feature, because it might complicate their certification procss. Also, the ones that do often use proprietory connectors. Here are a few cards that do provide for an external antenna:
Compex iWavePort WL11A+
ORiNOCO Gold card - proprietary connector
Zoom ZoomAir 4103 - RP-SMA connector