I just went into the Airport Utility->Your Base Station->Advanced->Port Mapping. Then you need to create a new "allowed" service by pressing the little + at the bottom of the list. Public and private UDP/TCP ports should all be the same, and should be in an acceptable range (use something in the 50,000-60,000 range). Enter your IP address (make a static one for your seeding machine) and click "Continue."
That "worked" for me, as I am visible in Azureus and to my tracker. There is one oddity though, when I am seeding, every 30 minutes or so, the base station oranges out (restarts). It pops back on in under 20 seconds, but it is a real hassle when I am playing xbox live or something.
Not a great router in my opinion, however 3 of my former Linksys WRT54s broke.. So maybe i'm just unlucky!
Happy Seeding.