There may be a specially designed adapter for your notebook. For example, my Evo N610c has an adapter that replaces the silver stripe on the notebook lid and does not use one of my PCMCIA slots.
However: any 802.11b capable PCMCIA card will work fine. Since you were planning on connecting to a wireless network, did you hava a particular on in mind? Do you know if it is just 802.11b (11MB, and very standard) or a faster variant (802.11g, which would also be able to talk down to 802.11b)? If you are planning on setting up in your home, get an 802.11g card and wireless router-hub (5 times faster) or Super-G/extreme-G (10 times faster than 802.11b). (By the way, my D-Link XtremeG *does* use a PCMCIA slot.) And, 802.11g has a slightly better renge.
Where? Best Buy, Circuit City, CompUSA, Home Depot, Radio Shack, Wal-Mart, OfficeMax, etc. To say this stuff is consumer mainstreamed is an understatement! Note that you may not find the fastest stuff other than at the big "toy" stores (Best Buy, Circuit City, CompUSA and the like).
If you do set up wireless at home, you should read about securing your base station <>. Change the default SSID, use WEP (or better) encryption, do not broadcast the SSID you choose, filter to only allow selected (your) MAC address, etc.