Yeah - real easy.
Plug in base station - configure with Mac (ssid and all that) -
connect PC, either via WiFi or by the ethernet cable on the back of the basestation - then you can either run a samba server on the Mac / connect via smb from the Mac / or use FTP to transfer files. You can easily mount a smb share on a mac, and have it appear on your desktop. I do this, and after 10.2 it works with no problems (10.0 and 10.1 were picky).
The old Airport/AirMac used Lucent Orinocco cards, but does anyone know what the make of the cards are for AirPort Extreme?
I used to use AirMac for a base station, but I've found LinkSys are actually better (better range) AND you can configure it with a web browser AND its cheaper! (And Apple wouldn't repair my AirMac after it blew up - they only said "might as well buy a new one" - it was out of warranty, so I bought a LinkSys)
-Wyrm