Hah, that's a good one. I haven't even touched mine.
Well, I'll do my best anyway...
First suggestion is to turn it off completely. The reason being that Macs don't have nearly as many security problems (not that I'm complaining, mind you) as a PC (especially on Windoze XP, from what I hear). No adware/spyware for us. No trojans. And we only have a minimal amount of virii compared to the amount that is available for PCs.

If, however, you do not like my first suggestion and prefer to retain a "better be safe than sorry attitude", then open the System Preferences application.
In there, click the Sharing icon and then the Firewall tab. (I bet that you've already figured those steps out since your firewall is already active, huh?).
Select "New...". In the "Port Name" drop-down box, select "Gnutella/Limewire", then click OK.
Restart LW to see if this had any effect.
(For reference, the port LW uses by default is 6346)

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iMac G4 OSX 10.3.9
RAM 256MB
LW 4.10.5 Basic
ADSL anything from 3 to 8Mbps/around 1024kbps

"Raise your can of Beer on high
And seal your fate forever
Our best years have passed us by
The Golden Age Of Leather"
-Blue Öyster Cult-