http://www.webopedia.com/TERM/W/Wi_Fi.html
http://en.wikipedia.org/wiki/Wifi
Seems that Wi-Fi is used when referring to 802.11.
Any 802.11g card should do fine. I'm in a similar situation as I've recently purchased a Nintendo DS which has WiFi, and now I need a router in order to play Mario Kart DS online. From what I've found out so far, any 802.11g card should be fine.
RJ