Never used the Proxim cards. They supposedly work with the Orinoco PC drivers but I've never tried myself. Don't think a mac would like them at all.
This however is the card you would need:
http://www.ebay.com/itm/Lucent-WiFi-Orinoco-11Mbit-s-Gold-PCMCIA-Card-/221203999477?pt=LH_DefaultDomain_2&hash=item3380c92af5
I also recommend trying with the lastest AirPort software installed. Legend has it that the latest AirPort driver sees the card as an Apple AirPort card, which in a way makes sense because they are the same card internally but Apple removed the external antenna, reflashed it to a point you can't flash it back and rebadged the exterior.