I just joined the forums to find out the same thing. I am behind a NAT router, but I do have forced IP enabled in Limewire and on my router, port 6346 forwarded to this Mac. Versions of Limewire up to 2.0 worke fine. People can grab my files without any problems. Version 2.0 and later doesn't work.

So what's the deal? Are there other undocumented ports that need to be forwarded? Did uploading in 2.X Mac get broken, and nobody has complained?