My PC has dual PCMCIA slots. Are these identical in functionality? My Linksys wireless card only works in the top slot.

usually, when 2 pcmcia slots are present, one is different.
there is a feature called ZV (zoom video) that allows more bandwith to pass on the pcmcia connector allowing heavy data stream (like video capture or mpeg decoder).
Possibly, some slots are multi voltage aware, while other are not.
Some PCMCIA card are working with 3.3v , others with 5v.
you have to read the user manual to confirm this.

http://www.pcmcia.org/pccard.htm

Thanks for that info and link Giroud. It was very helpful!