The listening port must be the same as the port that you've allowed for Gnutella within your software firewall & also the same as the port used if you manually port forward. The default port is 6346. You can change ports if you need to (eg if an ISP is blocking or filtering certain ports).

I'm port forwarding through my modem but still have a dynamic IP. As far as I know, the static IP is only for the device you're forwarding a port through. Is the other computer using LW too? I'm not sure whether you'd need to set up a second static IP if the other comp isn't using LW. But I know pretty much nothing about networks... I've asked someone to take a look at this when he's online next.

You can do a speed test here
http://www.dslreports.com/speedtest?more=1

Also, try downloading a file from here & see what speed you get
http://www.magnetmix.com/video.shtml

Remember that you can only download as fast as your connection & the other host's connection will allow. So try to download from multiple hosts with 4 star connections. Some ISPs do use traffic shaping to limit bandwidth for p2p... did you find out who your ISP is?

This thread has a lot of info about configuring LW for best performance, this can sometimes help to increase download speed
Configuring LW for best performance