Is usually very easy to enable Windoze laptop cards on an Airport station: the whole point of 802.11b is that it's a cross-platform standard...
The trick is to generate a password for WEP on the base station with a Mac, and the software will make the Hex key for you. Then you have to copy this Hex'd version of the password into the PC card's settings (usually in a place called Key #1). Then you should be able to connect.
You might have a problem if your laptop's card can't do encryption, but any recent card should be able to do at least 40bit. Check out Macwindows for more good info on this:
http://www.macwindows.com/airportpc.html