I'm the original poster. Sorry I was too rushed to register.

In OS X.2, or Jaguar, there's a Gnutella/Limewire setting for opening port 6346. Under System Prefs. > Sharing, click on your Firewall tab, and click the New button. You'll see a drop down menu with AOL at the top. Pull down to Gnutella/Limewire. It should now appear checked in the Firewall tab. Good to go.

The Airport user may have enabled WEP in his/her Airport Admin, possibly disabling sharing? I think you want WEP on though.

Anyway, I think it's nice there's all these Mac users who *want* to share files. Most of my friend won't.