Hi,
Since you have MacOS X and I assume you are running Win 2k or Win XP, it is easy to network yor Mac and Win for file sharing.
Start by skipping the AirPort, concent your Mac to the router via EEthernet cable. Go to System Preferance choose Network and select Build-in Ethernet. In the Configure IPv4 select Using DHCP. Keep the DHCP enabled on your router. The MAc will find an IP address. Make sure set any folders and/or files to share. You Mac must be in the same work group as you Win PCs. Then you are all set.
Richard.