Upload starts, connection craps out

I just recently started using Limewire. Maybe somebody can help me with this problem, since I want to give back as much to the community as I get out of it.
I am running Limewire 2.5 on Mac OS 10.1.5 and a dial up connection. I am using Norton Personal Firewall, however I set it to allow all access to the Limewire port 6346.
Now here's the problem: Searching and downloading works great for the most part (albeit fairly slow, as I expected), however whenever an upload from my machine starts, the connection breaks down (incl. my own downloads in progress). I've tried changing bandwidth percentage settings, number of connections/slots, still the same: Everything just gets stuck at 0 KB/sec and the connection is severed.
Does anybody have an idea what to do? I hate being a leach!