theres alot of inexpensive usb devices that would work fine. as far as pcmcia cards go, there is a wide variety. off the link that the guy above me posted, there is a link to the "ioxperts page". they make a pay-driver that you can demo but must pay in order to continue using it. there are free drivers but if u want the easy way the ioxperts is your best bet.
for the pcmcia card connection tool I use, i believe there is also a list of compatible cards.
http://wirelessdriver.sourceforge.net/faq.html
scroll down the page a bit and you will see a list. i use a WAVELAN silver (11b)(also known as orinoco silver) it also has a jack for an external antenna (range extension).
either way, you need a seperate utility for a pcmcia card, the "AirPort" thing in the upper bar is for the internal AP/APX card. some cards can be purchased quite cheap. make sure the card you buy it compatible with the wireless security of your network as well. There is still no WPA support (yet) in respect to the Wirelessdriver utility. Only 64/128bit WEP / AirPort password