Well, here's a bit of an explanation:

The download mesh is very interesting and powerful part of the gnutella protocol--and it needs no central server.

When you exchange a file, you also exchange a list of others who have that file (or a piece of it). So, as soon as you download a piece, you are letting others know that it's available and the

If you have tooltips turned on, you can see the number of "altlocs", or recent alternate locations by hovering the mouse over the download.

Your LW will be constantly checking and updating the list, requesting pieces from the best hosts it can find, and letting others know if a host is no longer a "good" altloc.

Pretty impressive, but way beyond my knowledge of exactly what is going on