The thing with the Gnutella Network is that many hosts are unable to upload faster than 20kB/s (kilobytes) although if you truly meant 20 kb/s(kilobits) that is very slow. If you are getting files off multiple sourses .. they should be faster I would have thought. If you are downloading from or uploading to a slower connection , that connection will dictate the speed.
Try going to
http://magnetmix.com/ and downloading a file from there as this will give you an idea of the speed LW is capable of. You may not actualy be able to open the file as Mac support is afaik still in the planning stage
It might be worth trying the vlc player for avi files , although you may of course have got a faulty file.
http://www.videolan.org/vlc/
To show the Navigation items, go to the View menu > show/hide and mark a tick against the unticked items.
let us know if this helps.