Heh. After browsing here some more, I found an EXCELLENT answer to the above questions. I'm including it here for completeness, in case someone later stumbles across this thread attempting the same thing I am.
The best part? Tesserex strikes again (only in a different thread)! I'm in awe. Thanks again, T!
"Here are the basic steps for port mapping on the 802.11g AirPort Extreme Base Station (AEBS)
Assign a manual IP to the host device
System Preferences > Network > Show > AirPort > TCP/IP
o Configure IPv4: Manually
o IP Address: <choose an IP address outside of the AEBS's DHCP range: 10.0.1.2 - 10.0.1.200>
o Subnet Mask: 255.255.255.0
o Router: 10.0.1.1
o DNS Servers <your ISP DNS server IPs>
Setup Port Mapping on the AEBS
To setup port mapping on an AEBS, either connect to the AEBS's wireless network or, temporarily, connect directly, using an Ethernet cable, to the LAN port of the AEBS, and then use the AirPort Admin Utility to change these settings:
Port Mapping tab
o Click "Add"
o Public Port: <enter the Port # which will be accessed from the Internet>
o Private Address: <enter the static IP address from above>
o Private Port: <either enter the same value as the Public port or the value you want your application/service to answer on>
o Click "Ok"
o Repeat the last series of steps for each port you wish to map."
There's another thread that explains the terminology that I'm including as a reference:
http://discussions.apple.com/thread.jspa?messageID=6811661
Jeezus, if only Apple designed internet protocols, then none of this would be needed. :P